Background: Disease surveillance is critical for WHO’s Global Programme to Eliminate Lymphatic Filariasis (LF), but current field-ready diagnostics exhibit insufficient sensitivity and/or specificity in low-endemic settings. We aim to develop an ultra-sensitive and field-friendly CRISPR/Cas13-based SHERLOCK (Specific High-sensitivity Enzymatic Reporter unLOCKing) tool for point-of-care detection of Wuchereria bancrofti infection. Methods: The SHERLOCK assay was performed in two-step and one-pot formats with sensitivity compared to qPCR. Assays were validated using 149 pooled mosquito and 185 human blood samples from Samoa, which were previously tested for LF antigen using WHO-recommended Filariasis Test Strips (FTS) and microscopically examined for microfilariae (Mf). We also used lyophilised one-pot SHERLOCK master mix and assessed its thermostability after storage at 25°C, 4°C and -20°C. Findings: The W. bancrofti SHERLOCK assays achieved a detection limit of 0.1 fg/μL gBlock DNA and showed no cross-reaction with five other filarial species. For both mosquito and human samples, the two-step SHERLOCK assay reached 100% sensitivity and specificity, while one-pot SHERLOCK showed 94.0-96.4% sensitivity and 100% specificity. The lyophilised one-pot SHERLOCK mix maintained a detection limit of 10 fg/μL W. bancrofti gBlock after 10 days at 25°C, indicating reduced reliance on cold-chain for reagent storage and transport. However, when testing human blood samples with lyophilised SHERLOCK, reduced sensitivity (59.7%) was observed. Interpretation: This CRISPR-based platform offers a promising field-ready next-generation approach to LF diagnostics, potentially addressing current limitations, enhancing surveillance and elimination efforts.

BACKGROUND:Sensitive diagnostic tools that signal lymphatic filariasis (LF) transmission are needed to monitor the progress of LF elimination programs. Anti-filarial antibody (Ab) markers could be more sensitive than antigen (Ag) point-of-care tests for monitoring LF transmission in some settings. This study aimed to investigate the sensitivity of anti-filarial Abs for detecting signals of LF transmission in Samoa by i) investigating the sensitivity and specificity of Ab to identify Ag-positives; ii) estimating the average number needed to test (NNTestav) to identify LF-seropositives (seropositive for Ag and/or any Ab), and iii) compare the efficiency of the different serological indicators by target age group and sampling design. METHODS:A community-based serological survey of participants aged ≥5 years was conducted 1.5-3.5 months following the first round of triple-drug mass drug administration in Samoa in 2018, covering 35 primary sampling units (PSUs) (30 randomly selected and five purposively selected 'suspected hotspots'). Ag-positivity was detected using Alere Filariasis Test Strips, and Ab-seropositivity (Bm14, Wb123, Bm33 Abs) were measured using multiplex bead assays. Seroprevalence was adjusted for study design and standardised for age and gender. NNTestav was calculated using the formula 1/p, where p was the adjusted seroprevalence for each subgroup. RESULTS:Of 3795 participants (mean age: 20.7; 51.2% female), 1892 (49.9%) were LF-seropositive. If Ag alone was used to identify LF-seropositives, only 5% (117/1892) would be identified. Of the three Ab seromarkers, Bm14 Ab had the highest area under the Receiver-Operating Characteristic Curve ([ROC]=0.88) to classify participants as Ag-positive, followed by Wb123 Ab (ROC=0.83) and Bm33 Ab (ROC=0.76). Participants aged ≥10 years had lower NNTestav compared to participants aged 5-9 years for all seromarkers. NNTestav was lower in purposively versus randomly selected PSUs. CONCLUSIONS:All Ab seromarkers had high ROC values to classify patients as Ag-positive and may be useful tools for LF surveillance in some settings. However, further research is required to fully understand how best Ab serosurveillance can be incorporated into LF elimination programmes.

OBJECTIVES:The first round of triple-drug mass drug administration (MDA) for lymphatic filariasis (LF) in Samoa was in 2018. This study aims to i) examine progression of LF antigen (Ag) and microfilaria (Mf) in Ag-positive individuals from 2019-2023; and ii) compare Ag/Mf prevalence in household members of Mf-positive vs Mf-negative participants. METHODS:In 2023, we tested Ag-positive participants (indexes) from a 2019 survey in Samoa, and their household members. We tested for Ag (Alere/Abbott Filariasis Test Strip) and Mf. We examined changes in Ag/Mf status in index participants and compared Ag/Mf prevalence between household members of Mf-positive and Mf-negative indexes. RESULTS:We recruited 91 indexes and 317 household members. In 2023, all 17 Mf-positive indexes remained Ag-positive and 11/15 with Mf results (73.3%) were Mf-positive. Of 74 Mf-negative indexes, 79.7% remained Ag-positive in 2023 and 31.1% became Mf-positive. Household members of Mf-positive indexes were more likely to be Ag-positive (odds ratios 3.3, 95% CI 1.0-10.3) compared to those of Mf-negative indexes. CONCLUSION:Our results raise concerns regarding long-term effectiveness of a single-dose of triple-drug MDA for sustained clearance of Mf in Samoa. Guidelines for follow-up and treatment of Ag/Mf-positive people and household members are urgently required.

BACKGROUND:In Samoa, lymphatic filariasis (LF) remains endemic despite persistent elimination efforts. Targeted sampling based on locations of known infections could be an efficient strategy for locating infected individuals and residual infections to support these efforts. This cross-sectional study assesses the efficiency of reactive case detection versus random sampling for identifying LF antigen (Ag)- and microfilaria (Mf)-positive individuals in Samoa in varying Ag prevalence scenarios. METHODOLOGY:In 2023, six primary sampling units (PSUs) were surveyed using random and targeted sampling strategies. PSUs were selected based on Ag prevalence in 2019; two PSUs each with low (3-5%), medium (6-7%) and high (13-17%) Ag prevalence. The randomly selected group included residents aged ≥5 years in 15 houses per PSU. The targeted group included residents aged ≥5 years in up to eight households within 200 metres of a household where Ag-positive resident(s) were identified in 2019. Blood samples were tested for Ag and examined for Mf. PRINCIPAL FINDINGS:The targeted sampling strategy (n = 400 people) identified more positives (57 Ag-positive, 23 Mf-positive) than the random sampling strategy (n = 494, 39 Ag-positive, 16 Mf-positive), with an overall targeted:random sampled case ratio of 1.8 (95% CI 1.3-2.5) for Ag and 1.8 (95% CI 1.1-3.1) for Mf. Efficiency gains were greatest in medium prevalence PSUs for both Ag-positives (ratio = 2.4, 95% CI 1.3-5.2) and Mf-positives (ratio = 2.6, 95% CI 0.9-12.8). CONCLUSIONS:In Samoa, a targeted sampling strategy using reactive case detection was more efficient for locating Ag-positive and Mf-positive individuals compared to random sampling, with the highest efficiency gain in medium Ag prevalence settings. Our study demonstrates the value of testing household members of near neighbours of Ag-positive and helps to inform LF surveillance strategies in Samoa and the Pacific region by promoting more efficient resource allocation.

Multiplex bead immunoassays (MBA) can detect antibody responses to multiple antigens. Using MBA data from the Surveillance and Monitoring to Eliminate Lymphatic Filariasis (LF) and Scabies from Samoa (SaMELFS) 2018, we aim to estimate national seroprevalence of neglected tropical diseases (NTDs), vaccine-preventable diseases (VPDs), and arboviruses in Samoa. A community-based serosurvey of 3851 participants aged ≥ 5 years in 35 primary sampling units (PSUs). Using MBA, dried blood spots were assayed for antibodies (Ab) from 10 pathogens: LF, trachoma, yaws, tetanus, diphtheria, rubella, measles, dengue, Zika, and chikungunya. Seroprevalence was adjusted for study design, age, and gender. NTD seroprevalence for LF was 50.8% (Bm33 Ab), 32.0% (Wb123 Ab), 20.3% (Bm14 Ab); 5.5% for trachoma; and 1.0% (Tmpa Ab) and 0.2% (Rp17 Ab) for yaws. VPD seroprevalence was 91.0% for tetanus, 83.5% for diphtheria, 79.0% for rubella, and 43.6% for measles. Arbovirus seroprevalence for dengue was 91.1% (dengue virus serotype-1 [DENV-1]), 97.2% (DENV-2), 96.9% (DENV-3), 94.7% (DENV-4); 85.7% for Zika; and 57.0% for chikungunya. Increasing age was associated with seropositivity to NTDs, arboviruses, tetanus, and measles. Clustering was highest at the household level; the strongest clustering was for DENV-3 (intraclass correlation coefficient [ICC]:0.32), Bm33 Ab (ICC:0.31), and Bm14 Ab (ICC:0.31). Integrated serosurveillance can provide a comprehensive picture of population-level immunity to multiple diseases. Our investigation into associations with seroprevalence can aid the development of evidence-based prevention, control, and elimination strategies.

OBJECTIVES:Contrasting evidence is emerging on the long-term effectiveness of triple-drug therapy for elimination of lymphatic filariasis (LF) in the Pacific region. We evaluated the effectiveness of ivermectin, diethylcarbamazine and albendazole (IDA) for sustained clearance of microfilariae (Mf) in Samoa. METHODS:We enrolled two cohorts of Mf-positive participants. Cohort A were Mf-positive participants from 2018, who received directly observed triple-drug therapy in 2019 and were retested and retreated in 2023 and 2024. Cohort B were Mf-positive and treated in 2023 and retested in 2024. Participants were tested for LF antigen and Mf. RESULTS:In Cohort A, eight of the 14 participants from 2018/2019 were recruited in 2023; six were Mf-positive. In 2024, six participants were retested, and two were Mf-positive. Cohort B included eight participants, and two remained Mf-positive in 2024. Mf prevalence in 2023 for Cohort A (71.4%, 95% CI 29.0%-96.3%) was significantly higher than among their household members (12.0%, 95% CI 2.5%-31.2%). CONCLUSION:One or two doses of directly observed IDA was not sufficient for sustained clearance of Wuchereria bancrofti Mf in Samoa. The high Mf prevalence in treated individuals compared to household members suggests recrudescence rather than reinfection.

Background For lymphatic filariasis (LF) elimination, the World Health Organization recommends multiple rounds of mass drug administration (MDA). While LF antigen (Ag) is routinely used to monitor progress, recent evidence suggests more time-sensitive indicators are needed during the immediate post-MDA period. In Samoa, triple-drug MDA was distributed in 2018 and 2023. This study aimed to evaluate the impact of Samoa’s second round of triple-drug MDA on human and mosquito-based indicators. Methodology Surveys were conducted in eight primary sampling units (PSUs) in 2019 (7–9 months after the 2018 MDA), 2023 (4.5 years after the 2018 MDA) and 2024 (10 months after the 2023 MDA). Participants aged ≥5 years from randomly selected households were tested for Ag and microfilariae (Mf). For molecular xenomonitoring (MX), mosquitoes were caught using BG-Sentinel traps at households, sorted into pools by species, and tested for filarial DNA using quantitative polymerase chain reaction (qPCR). Results and key findings In 2024, Ag prevalence was 10.3% (95% CI:7.3-14.5) vs 9.9% (95% CI: 3.5-21.0) in 2023 and 9.8% (95% CI:5.6-15.5) in 2019. Mf prevalence was 3.1% (95% CI: 1.8-5.5) in 2024 vs 5.1% (95% CI:1.3-12.4) in 2023 and 3.1% (95% CI:1.3-5.9) in 2019. Odds ratios (OR) of a positive test in 2024 vs 2023 showed no decrease for Ag (OR 1.0; 95% CI:0.7-1.6), but a potential reduction in the proportion of Ag-positive participants who were Mf-positive (OR 0.6; 95% CI: 0.2-1.4) and a significant reduction in the prevalence of qPCR-positive mosquitoes (OR 0.4; 95%CrI: 0.2-0.7). From 2019-2024, there were reductions in prevalence of qPCR-positive Aedes spp. (OR 0.5; 95% CrI:0.3-1.0) and Aedes polynesiensis (OR 0.4; 95% CrI: 0.2-0.8). Conclusions In Samoa, LF transmission continues despite two rounds of triple-drug MDA five years apart. Mosquito indicators can provide a more sensitive measure of MDA impact in the immediate post-intervention period and complement human indicators for long-term surveillance. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement Yes ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Ethics approvals were granted by the Samoa Ministry of Health and The University of Queensland Human Research Ethics Committee (protocols 2021/HE000895 and 2024/HE001263). The study was conducted in close collaboration with the Samoa Ministry of Health, the WHO country office in Samoa, and the Samoa Red Cross. Permission was sought from village leaders before entering a village. Verbal and written informed consent were obtained from all participants and from the parents or guardians of participants under the age of 18 years. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Data used in this study were collected during field surveys conducted in Samoa. Communities in Samoa are small, and sharing individual-level human data could enable identification of participants, which would violate the conditions of the study’s ethics approvals. As a result, individual-level human data are not publicly available. Requests for access to de-identified individual-level data may be made to the Human Research Ethics Committee at The University of Queensland (humanethics{at}research.uq.edu.au), citing protocols 2021/HE000895 and 2024/HE001263, and will be considered subject to ethical approval and data sharing agreements. All relevant aggregated data required to interpret the findings of this study, including primary sampling unit–level estimates for human and mosquito indicators, are provided in the Supplementary Material.

Introduction: Seroprevalence of antibodies for vaccine-preventable diseases (VPDs), due to vaccination or previous infection, can provide a more accurate estimate of immunity compared to vaccination coverage data alone. This study aimed to examine the seroepidemiology and spatial distribution of VPD seroprevalence in Samoa in 2018 and 2019. Methods: Dried blood spot (DBS) samples were collected from two nationally representative community-based surveys of participants aged ≥5 years from the Surveillance and Monitoring to Eliminate Lymphatic Filariasis and Scabies from Samoa (SaMELFS) project. DBSs were tested using multiplex bead assays (MBAs) to detect antibodies against measles, rubella, diphtheria, and tetanus. Seroprevalence was estimated at the national and primary sampling unit (PSU) levels, and cluster analysis was completed using SaTScan. Results: Overall, 8394 valid MBA results were analysed across 35 PSUs. The highest overall seroprevalence was observed for tetanus (91.0%; 95% CI: 90.2–91.7), followed by diphtheria (83.7%; 95% CI: 82.7–84.7), rubella (79.3%; 95% CI: 78.2–80.3), and measles (45.8%; 95% CI: 44.8–46.9) with substantial heterogeneity across PSUs. Clusters of seronegativity to measles (relative risk [RR]: 1.16, p < 0.001) and diphtheria (RR: 1.16, p < 0.001) were also identified. Conclusions: These findings demonstrate significant variation in seroprevalence and pockets of low population immunity to multiple VPDs, highlighting the key advantage of an integrated rather than siloed approach. The relatively high seroprevalence to rubella suggests potential community transmission, emphasising the need to strengthen congenital rubella surveillance and improve vaccination coverage. Identifying low immunity to VPDs can provide an early warning to potential outbreak risk and support the Ministry of Health to target public health interventions in higher-risk areas.

BackgroundLymphatic filariasis (LF) is a globally significant, vector-borne, neglected tropical disease that can result in severe morbidity and disability. As the World Health Organization (WHO) Global Programme to Eliminate Lymphatic Filariasis makes progress towards LF elimination, there is greater need to develop sensitive strategies for post-intervention surveillance. Molecular xenomonitoring (MX), the detection of pathogen DNA in vectors, may provide a sensitive complement to traditional human-based surveillance techniques, including detection of circulating filarial antigen and microfilaraemia (Mf). This study aims to explore the relationship between human Mf prevalence and the prevalence of polymerase chain reaction (PCR)-positive mosquitoes using MX.MethodsThis study compared Mf and MX results from a 2019 community-based survey conducted in 35 primary sampling units (PSUs) in Samoa. This study also investigated concordance between presence and absence of PCR-positive mosquitoes and Mf-positive participants at the PSU level, and calculated sensitivity and negative predictive values for each indicator using presence of any Mf-positive infection in humans or PCR-positive mosquitoes as a reference. Correlation between prevalence of filarial DNA in mosquitoes and Mf in humans was estimated at the PSU and household/trap level using mixed-effect Bayesian multilevel regression analysis.ResultsMf-positive individuals were identified in less than half of PSUs in which PCR-positive mosquito pools were present (13 of 28 PSUs). Prevalence of PCR-positive mosquitoes (each species separately) was positively correlated with Mf prevalence in humans at the PSU level. Analysed at the species level, only Aedes polynesiensis demonstrated strong evidence of positive correlation (r) with human Mf prevalence at both PSU (r: 0.5, 95% CrI 0.1-0.8) and trap/household levels (r: 0.6, 95% CrI 0.2-0.9).ConclusionsFindings from this study demonstrate that MX can be a sensitive surveillance method for identifying residual infection in low Mf prevalence settings. MX identified more locations with signals of transmission than Mf-testing. Strong correlation between estimated PCR-positive mosquitoes in the primary vector species and Mf in humans at small spatial scales demonstrates the utility of MX as an indicator for LF prevalence in Samoa and similar settings. Further investigation is needed to develop MX guidelines to strengthen the ability of MX to inform operational decisions.

Background Elimination of lymphatic filariasis (LF) as a public health problem remains an ongoing challenge in the Pacific region. In 2018, Samoa was the first country to implement a national triple-drug mass drug administration (MDA) using ivermectin, diethylcarbamazine, and albendazole (IDA). This study reports on antigen (Ag) and microfilaria (Mf) prevalence in Samoa in 2019, 6-8 months post-MDA, and evaluates the effectiveness of the intervention in reducing Ag prevalence to below a 2% threshold. We also compared the change in Ag prevalence pre- and post-MDA between 5-9-year-olds and ≥10-year-olds to assess the suitability of young children as the target group for transmission assessment surveys (TAS). Methodology We surveyed 30 randomly selected and 5 purposefully selected primary sampling units (PSUs) in Samoa in 2018 (1.5-3.5 months post triple-drug MDA) and 2019 (6-8 months post triple-drug MDA). In each PSU, we conducted a community survey of 15-20 randomly selected households and a convenience survey of 5-9-year-old children. Demographic details were collected using an electronic questionnaire. A finger prick blood sample was collected from all participants to test for Ag and Mf. Prevalence estimates were adjusted for age, sex, and survey design. Principal Findings There was no significant change in adjusted Ag prevalence in the 30 randomly selected PSUs between 2018 (3.9% [95% CI: 2.7-5.6%]) and 2019 (4.1% [95% CI 2.7-5.9%]). In these PSUs, significantly higher Ag prevalence was observed in participants aged 10 ≥ years (4.6%, 95% CIs 3.0-6.7%) compared to 5-9-year-olds (1.1%, 95% CIs 0.5-2.2%). Conclusions/Significance  A single round of triple-drug MDA was insufficient to break LF transmission in Samoa 6-8 months post-MDA. Significantly higher Ag prevalence in participants ≥ 10 years old also supports existing evidence that basing elimination thresholds on Ag prevalence among 6-7-year-olds may not be the most suitable strategy for post-MDA surveillance. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement Yes ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Ethics approval was obtained from Human Research Ethics Committees at the Samoa Ministry of Health and The Australian National University (protocol 2018/341) and ratified by the University of Queensland Human Research Ethics Committee (protocol 2021/HE000895). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Data used in this paper were collected during field surveys in Samoa. Communities in Samoa are small (some with less than 200 inhabitants) and sharing individual level data could enable identification of individual participants, and violating the conditions of the study’s ethics approval. For requests relating to data access, please contact the Human Ethics Department at the University of Queensland (humanethics@research.uq.edu.au) citing protocol 2021/HE000895. All relevant data at the primary sampling unit level has been included in the supplementary material.

Background Lymphatic filariasis (LF) remains a significant global issue. To eliminate LF as a public health problem, the World Health Organization (WHO) recommends multiple rounds of mass drug administration (MDA). In certain scenarios, including when elimination targets have not been met with two-drug MDA, triple-drug MDA (using ivermectin, diethylcarbamazine and albendazole) is recommended. In this study, we report on antigen (Ag) and microfilaria (Mf) prevalence in eight primary sampling units (PSUs) in Samoa 4.5 years after one round of triple-drug MDA. Methodology In 2023, community surveys were conducted in eight PSUs that had been surveyed previously in 2018 (between 1.5 and 3.5 months post triple-drug MDA) and 2019 (six to eight-months post triple-drug MDA). Fifteen houses were randomly selected in each PSU with household members aged ≥ 5 years invited to participate. Blood samples were tested for Ag and Mf. Principal findings Ag-positive participants were observed in six of the eight PSUs, and Ag prevalence was significantly above the 1% threshold in four PSUs. The presence of Mf-positive participants in five PSUs confirms the presence of residual active infections. Conclusions/Significance This study provides evidence of persistent LF transmission in Samoa 4.5 years after one round of triple-drug MDA, confirming that one round was insufficient for interruption of transmission in this setting. Our findings highlight the negative impact of delaying MDA rounds, for example, due to public health emergencies.

Background To monitor the progress of lymphatic filariasis (LF) elimination programmes, field surveys to assess filarial antigen (Ag) prevalence require access to reliable, user-friendly rapid diagnostic tests. We aimed to evaluate the performance of the new Q Filariasis Antigen Test (QFAT) with the currently recommended Filariasis Test Strip (FTS) for detecting the Ag of Wuchereria bancrofti, the causative agent of LF, under field laboratory conditions. Methodology/Principal findings During an LF survey in Samoa, 344 finger-prick blood samples were tested using FTS and QFAT. Microfilariae (Mf) status was determined from blood slides prepared from any sample that reported Ag-positive by either Ag-test. Each test was re-read at 1 hour and the next day to determine the stability of results over time. Overall Ag-positivity by FTS was 29.0% and 30.2% by QFAT. Concordance between the two tests was 93.6% (kappa = 0.85). Of the 101 Mf slides available, 39.6% were Mf-positive, and all were Ag-positive by both tests. Darker test line intensities from Ag-positive FTS were found to predict Mf-positivity (compared to same/lighter line intensities). QFAT had significantly higher reported test result changes than FTS, mostly reported the next day, but fewer changes were reported between 10 minutes to 1hour. The field laboratory team preferred QFAT over FTS due to the smaller blood volume required, better usability, and easier readability. Conclusion/Significance QFAT could be a suitable and user-friendly diagnostic alternative for use in the monitoring and surveillance of LF in field surveys based on its similar performance to FTS under field laboratory conditions.

The elimination of lymphatic filariasis (LF) as a public health problem remains an ongoing challenge in the Pacific region. This study reports on antigen (Ag) and microfilaria (Mf) prevalence in Samoa in 2019, 7–9 months after the completion of the first round of triple-drug mass drug administration (MDA). It evaluates the effectiveness of the intervention for reducing Ag prevalence to below a 2% threshold, and how this differs between 5–9-year-olds and ≥10-year-olds. We surveyed 30 randomly selected and five purposefully selected primary sampling units (PSUs) in Samoa in 2018 (1–3 months post-triple-drug MDA) and, again, in 2019. In each PSU, we conducted a community survey of 15–20 households and a convenience survey of 5–9-year-old children. A finger-prick blood sample was collected from all participants to test for Ag and Mf. Demographic details were also collected. There was no significant change in adjusted Ag prevalence in the 30 randomly selected PSUs between 2018 (3.9% [95% CI: 2.7–5.6%]) and 2019 (4.1% [95% CI 2.7–5.9%]). Significantly higher Ag prevalence was observed in participants aged ≥10 years (4.6%, 95% CIs 3.0–6.7%) compared to 5–9-year-olds (1.1%, 95% CIs 0.5–2.2%), supporting existing evidence that post-MDA surveillance should not be based on Ag prevalence among 6–7-year-olds. A single round of triple-drug MDA was insufficient to break LF transmission in Samoa 7–9 months post-MDA.

Background In Samoa, lymphatic filariasis (LF) remains endemic. Targeted sampling strategies based on the locations of known infections could be more efficient, and therefore cost-effective, than random sampling for locating infected individuals and hotspots, providing valuable information to develop more efficient and effective interventions. The added efficiency of these strategies may depend on the prevalence of the chosen indicator in the area being surveyed. This study aims to assess the efficiency of targeted versus random sampling for identifying LF antigen (Ag)- and microfilaria (Mf)-positive individuals in Samoa across varying background Ag prevalence levels. Methodology In 2023, six primary sampling units (PSUs) were surveyed using random and targeted sampling strategies. PSUs were selected based on Ag prevalence in 2019, including two low (3-5%), medium (6-7%) and high Ag prevalence (13-17%). The randomly selected group included residents aged ³5 years in 15 houses per PSU. The targeted group included residents aged ³5 years in up to eight households within 200 metres of a household where Ag-positive resident(s) were identified in 2019.  Finger prick blood samples were tested for Ag and Ag-positive samples were examined for microfilaria (Mf). Principal Findings The targeted sampling strategy (n=400 people) identified more positives (57 Ag-positive, 23 Mf-positive) than the random sampling strategy (n=494, 39 Ag-positive, 16 Mf-positive), with an overall targeted:random sampled case ratio of 1.8 (95% CI 1.3-2.5) for Ag and 1.8 (95% CI 1.1-3.1) for Mf. Gain in efficiency was greatest in medium prevalence PSUs for both Ag-positives (ratio=2.4, 95% CI 1.3-5.2) and Mf-positives (ratio=2.6, 95% CI 0.9-12.8). Conclusions In Samoa, a targeted sampling strategy was a more efficient method for locating Ag-positive and Mf-positive individuals compared to random sampling, with the highest efficiency gain in medium Ag prevalence settings. The findings have design implications for LF surveillance in Samoa and other Pacific Island countries. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement Yes ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Ethics approvals were obtained from the Samoa Ministry of Health and The University of Queensland Human Research Ethics Committee (protocol 2021/HE000895). The study was conducted in close collaboration with the Samoa Ministry of Health, the World Health Organization (WHO) country office in Samoa, and the Samoa Red Cross. Prior to entering a village, permission was granted from village leaders to conduct the study. Verbal and written informed consent were obtained for all participants, or from the parents or guardians of participants who were less than 18 years old. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Data used in this paper were collected during field surveys in Samoa. Communities in Samoa are small (some with less than 200 inhabitants) and sharing individual level data could enable identification of individual participants, and violating the conditions of the study’s ethics approval. For requests relating to data access, please contact the Human Ethics Department at the University of Queensland (humanethics@research.uq.edu.au) citing protocol 2021/HE000895”. if you would like access to the data. All relevant data at the primary sampling unit level has been included in the supplementary material.

Background:The Global Typhoid Genomics Consortium was established to bring together the typhoid research community to aggregate and analyse Salmonella enterica serovar Typhi (Typhi) genomic data to inform public health action. This analysis, which marks 22 years since the publication of the first Typhi genome, represents the largest Typhi genome sequence collection to date (n=13,000). Methods:This is a meta-analysis of global genotype and antimicrobial resistance (AMR) determinants extracted from previously sequenced genome data and analysed using consistent methods implemented in open analysis platforms GenoTyphi and Pathogenwatch. Results:Compared with previous global snapshots, the data highlight that genotype 4.3.1 (H58) has not spread beyond Asia and Eastern/Southern Africa; in other regions, distinct genotypes dominate and have independently evolved AMR. Data gaps remain in many parts of the world, and we show the potential of travel-associated sequences to provide informal 'sentinel' surveillance for such locations. The data indicate that ciprofloxacin non-susceptibility (>1 resistance determinant) is widespread across geographies and genotypes, with high-level ciprofloxacin resistance (≥3 determinants) reaching 20% prevalence in South Asia. Extensively drug-resistant (XDR) typhoid has become dominant in Pakistan (70% in 2020) but has not yet become established elsewhere. Ceftriaxone resistance has emerged in eight non-XDR genotypes, including a ciprofloxacin-resistant lineage (4.3.1.2.1) in India. Azithromycin resistance mutations were detected at low prevalence in South Asia, including in two common ciprofloxacin-resistant genotypes. Conclusions:The consortium's aim is to encourage continued data sharing and collaboration to monitor the emergence and global spread of AMR Typhi, and to inform decision-making around the introduction of typhoid conjugate vaccines (TCVs) and other prevention and control strategies. Funding:No specific funding was awarded for this meta-analysis. Coordinators were supported by fellowships from the European Union (ZAD received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 845681), the Wellcome Trust (SB, Wellcome Trust Senior Fellowship), and the National Health and Medical Research Council (DJI is supported by an NHMRC Investigator Grant [GNT1195210]).

Background Scabies is a common skin infestation caused by the Sarcoptes scabei mite. Ivermectin, one of three drugs used in mass drug administration (MDA) for lymphatic filariasis, is also effective for treating scabies. Ivermectin-based MDA was first conducted in Samoa in August 2018, with ivermectin being offered to those aged ≥5 years. Here, we report scabies prevalence in Samoa after MDA. Methods We conducted household surveys 1.5–3.5 months (Survey 1) and 6–8 months (Survey 2) after the 2018 MDA in 35 primary sampling units. We conducted clinical examination for scabies-like rash and used International Alliance for the Control of Scabies classification criteria. We estimated scabies prevalence by age, gender and region. Multivariable logistic regression was used to assess factors associated with prevalence. Results We surveyed 2868 people (499 households) and 2796 people (544 households) aged 0–75 years in Surveys 1 and 2, respectively. Scabies prevalence increased from 2.4% (95% CI 2.1–2.7%) to 4.4% (95% CI 4.0–4.9%) between surveys. Scabies was associated with younger age (0–4 years: aOR 3.5 [2.9–4.2]; 5–15 years: aOR 1.6 [1.4–1.8] compared to ≥16 years), female gender (aOR 1.2 [95% CI 1.1–1.4]; region (aOR range from 1.4 [1.1–1.7] to 2.5 [2.1–3.1] between regions), large households (aOR 2.6 [2.0–3.4] households ≥13), and not taking MDA in 2018 (aOR 1.3 [95% CI 1.1–1.6]). Conclusions We found moderate prevalence of scabies in two population-representative surveys conducted within 8 months of the 2018 MDA for lymphatic filariasis. Prevalence appeared to increase between the surveys, and ongoing surveillance is recommended, particularly in young children.

Approximately 90% of chronic typhoid carriers with persistent Salmonella enterica serovar Typhi (S. Typhi) gallbladder infection have gallstones. In Samoa, where typhoid fever has been endemic for many decades, risk factors predisposing to the development of gallstones are increasing among adults. The Samoa Typhoid Fever Control Program dispatches a "Typhoid Epidemiologic SWAT Team" to perform a household investigation of every blood culture-confirmed case of acute typhoid fever. Investigations include screening household contacts to detect chronic carriers. Following limited training, two nonexpert ultrasound operators performed point-of-care ultrasound (POCUS) on 120 Samoan adults from August to September 2019 to explore the feasibility of POCUS to detect individuals with gallstones during household investigations and community screenings. POCUS scans from 120 Samoan adults in three cohorts (28 food handlers, two typhoid cases and their 18 household contacts, and 72 attendees at an ambulatory clinic) were reviewed by a board-certified radiologist who deemed 96/120 scans (80%) to be interpretable. Compared with the radiologist (gold standard), the nonexpert operators successfully detected 6/7 Samoans with gallstones (85.7% sensitivity) and correctly identified 85/89 without gallstones (95.5% specificity). The proportion (24/120) of uninterpretable scans from this pilot that used minimally trained clinicians (who are neither radiologists nor ultrasound technicians) indicates the need for additional training of POCUS operators. Nevertheless, this pilot feasibility study engenders optimism that in the Samoan setting nonexperts can be trained to use POCUS to diagnose cholelithiasis, thereby helping (along with stool cultures and Vi serology) to identify possible chronic S. Typhi carriers.

Salmonella enterica serovar Typhi (S. Typhi) is either widely distributed or proximally transmitted via fecally-contaminated food or water to cause typhoid fever. In Samoa, where endemic typhoid fever has persisted over decades despite water quality and sanitation improvements, the local patterns of S. Typhi circulation remain unclear. From April 2018-June 2020, epidemiologic data and GPS coordinates were collected during household investigations of 260 acute cases of typhoid fever, and 27 asymptomatic shedders of S. Typhi were detected among household contacts. Spatial and temporal distributions of cases were examined using Average Nearest Neighbor and space-time hotspot analyses. In rural regions, infections occurred in sporadic, focal clusters contrasting with persistent, less clustered cases in the Apia Urban Area. Restrictions to population movement during nationwide lockdowns in 2019-2020 were associated with marked reductions of cases. Phylogenetic analyses of isolates with whole genome sequences (n = 186) revealed one dominant genotype 3.5.4 (n = 181/186) that contains three Samoa-exclusive sub-lineages: 3.5.4.1, 3.5.4.2, and 3.5.4.3. Variables of patient sex, age, and geographic region were examined by phylogenetic groupings, and significant differences (p<0.05) associated genetically-similar isolates in urban areas with working ages (20-49 year olds), and in rural areas with age groups typically at home (<5, 50+). Isolates from asymptomatic shedders were among all three sub-lineages. Whole genome sequencing provided evidence of bacterial genetic similarity, which corroborated 10/12 putative epidemiologic linkages among cases and asymptomatic shedders, as well as 3/3 repeat positives (presumed relapses), with a median of one single nucleotide polymorphism difference. These findings highlight various patterns of typhoid transmission in Samoa that differ between urban and rural regions as well as genomic subtypes. Asymptomatic shedders, detectable only through household investigations, are likely an important reservoir and mobile agent of infection. This study advances a "Samoan S. Typhi framework" that supports current and future typhoid surveillance and control efforts in Samoa.

Molecular xenomonitoring (MX), the detection of filarial DNA in mosquitoes using molecular methods (PCR), is a potentially useful surveillance strategy for lymphatic filariasis (LF) elimination programs. Delay in filarial antigen (Ag) clearance post-treatment is a limitation of using human surveys to provide an early indicator of the impact of mass drug administration (MDA), and MX may be more useful in this setting. We compared prevalence of infected mosquitoes pre- and post-MDA (2018 and 2019) in 35 primary sampling units (PSUs) in Samoa, and investigated associations between the presence of PCR-positive mosquitoes and Ag-positive humans. We observed a statistically significant decline in estimated mosquito infection prevalence post-MDA at the national level (from 0.9% to 0.3%, OR 0.4) but no change in human Ag prevalence during this time. Ag prevalence in 2019 was higher in randomly selected PSUs where PCR-positive pools were detected (1.4% in ages 5–9; 4.8% in ages ≥10), compared to those where PCR-positive pools were not detected (0.2% in ages 5–9; 3.2% in ages ≥10). Our study provides promising evidence for MX as a complement to human surveys in post-MDA surveillance.