The spread of multidrug-resistant bacteria from humans or livestock is a critical issue. However, the epidemiology of resistant pathogens across wastewater pathways is poorly understood. Therefore, we performed a detailed comparison of third-generation cephalosporin-resistant Escherichia coli (3GCREC) from wastewater treatment plants (WWTPs) to analyze dissemination pathways. A total of 172 3GCREC isolated from four WWTPs were characterized via whole genome sequencing. Clonal relatedness was determined using multi-locus sequence typing (MLST) and core genome MLST. Resistance genotypes and plasmid replicons were determined. A total of 68 MLST sequence types were observed with 28 closely related clusters. Resistance genes to eight antibiotic classes were detected. In fluoroquinolone-resistant isolates, resistance was associated with three-or-more point mutations in target genes. Typing revealed high genetic diversity with only a few clonal lineages present in all WWTPs. The distribution paths of individual lines could only be traced in exceptional cases with a lack of enrichment of certain lineages. Varying resistance genes and plasmids, as well as fluoroquinolone resistance-associated point mutations in individual isolates, further corroborated the high diversity of 3GCREC in WWTPs. In total, we observed high diversity of 3GCREC inside the tested WWTPs with proof of resistant strains being released into the environment even after treatment processes.

Epidemiological studies show that the care of patients in rooms with a previous stay by a person with evidence of multi-resistant pathogens (MRP) is associated with an increased risk of these pathogens occurring. The question therefore regularly arises as to whether MRP also exhibit resistance to the disinfectants used. To date, there are no standardised definitions for "resistance" to disinfectants. However, disinfectants authorised on the market are also effective against multi-resistant pathogens and the failure of efficient disinfection is mainly caused by application errors (insufficient cleaning, incomplete wetting, incorrect application concentration or exposure time etc.). The effectiveness of disinfectants depends on a variety of environmental factors (especially accompanying contamination). A reduced sensitivity to disinfectants can occur in individual isolates due to selection under sub-inhibitory concentrations of disinfectants. Resistance mechanisms to antibiotics do not mediate cross-resistance to disinfectants, but a change in the permeability of bacterial cells can influence sensitivity to disinfectants and antibiotics. In general, the success of routine disinfection can be improved by suitable process controls and contribute to reducing the transmission of MRP.

Asymptomatic long-term carriers of Shigatoxin producing Escherichia coli (STEC) are regarded as potential source of STEC-transmission. The prevention of outbreaks via onward spread of STEC is a public health priority. Accordingly, health authorities are imposing far-reaching restrictions on asymptomatic STEC carriers in many countries. Various STEC strains may cause severe hemorrhagic colitis complicated by life-threatening hemolytic uremic syndrome (HUS), while many endemic strains have never been associated with HUS. Even though antibiotics are generally discouraged in acute diarrheal STEC infection, decolonization with short-course azithromycin appears effective and safe in long-term shedders of various pathogenic strains. However, most endemic STEC-strains have a low pathogenicity and would most likely neither warrant antibiotic decolonization therapy nor justify social exclusion policies. A risk-adapted individualized strategy might strongly attenuate the socio-economic burden and has recently been proposed by national health authorities in some European countries. This, however, mandates clarification of strain-specific pathogenicity, of the risk of human-to-human infection as well as scientific evidence of social restrictions. Moreover, placebo-controlled prospective interventions on efficacy and safety of, e.g., azithromycin for decolonization in asymptomatic long-term STEC-carriers are reasonable. In the present community case study, we report new observations in long-term shedding of various STEC strains and review the current evidence in favor of risk-adjusted concepts.

Epidemiological studies show that the care of patients in rooms with a previous stay by a person with evidence of multi-resistant pathogens (MRP) is associated with an increased risk of these pathogens occurring. The question therefore regularly arises as to whether MRP also exhibit resistance to the disinfectants used. To date, there are no standardised definitions for "resistance" to disinfectants. However, disinfectants authorised on the market are also effective against multi-resistant pathogens and the failure of efficient disinfection is mainly caused by application errors (insufficient cleaning, incomplete wetting, incorrect application concentration or exposure time etc.). The effectiveness of disinfectants depends on a variety of environmental factors (especially accompanying contamination). A reduced sensitivity to disinfectants can occur in individual isolates due to selection under sub-inhibitory concentrations of disinfectants. Resistance mechanisms to antibiotics do not mediate cross-resistance to disinfectants, but a change in the permeability of bacterial cells can influence sensitivity to disinfectants and antibiotics. In general, the success of routine disinfection can be improved by suitable process controls and contribute to reducing the transmission of MRP.

The widespread dissemination of carbapenem-resistant bacteria in wastewater systems, particularly from clinical sources, poses a significant public health risk. This study assessed the concentrations and distributions of extracellular DNA (exDNA) and intracellular DNA (iDNA) harboring carbapenemase genes in wastewater from six tertiary care hospitals in Germany.We collected a total of 36 samples, comprising six biological replicates from each hospital, and analysed them using quantitative real-time PCR (qPCR) and digital PCR (dPCR). The analysis targeted seven carbapenemase genes: blaNDM, blaKPC, blaIMP, blaVIM, blaOXA-23-like, blaOXA-48-like, and blaOXA-58-like across both DNA fractions.Our results revealed significant variability in the concentrations of exDNA and iDNA across the sampling sites, with iDNA typically present at higher concentrations. Using NanoDrop One spectrophotometry and the Qubit dsDNA kit, exDNA concentrations ranged from 2.7 to 7.7 ng/mL, while Qubit recorded lower values between 1.1 and 4.0 ng/mL. Conversely, iDNA concentrations were markedly higher, spanning from 42.3 to 191.7 ng/mL with NanoDrop and 12.0 to 46.5 ng/mL with Qubit, highlighting the variability between DNA types and quantification methods. Despite its lower concentrations, exDNA comprised up to 18.2 % of total DNA, highlighting its potential role in the horizontal transfer of antimicrobial resistance genes (ARGs).The study detected target ARGs in both DNA fractions at all sites, with notable differences in their concentrations; iDNA consistently exhibited higher levels of ARGs, with the highest concentrations reaching 10.57 ± 0.20 log gene copies per liter (GC/L) for blaVIM in iDNA and 6.96 ± 0.72 log GC/L for blaIMP in exDNA. dPCR demonstrated greater sensitivity than qPCR, especially effective for detecting low-abundance targets like blaOXA-23-like in the exDNA fraction. Additionally, qPCR's susceptibility to inhibition and contamination emphasizes the superior robustness of dPCR.This research highlights the need for improved monitoring and the implementation of advanced treatment technologies to mitigate ARG dissemination in wastewater.

BACKGROUND:Antimicrobial materials or surfaces are advertised as part of infection prevention bundles. However, the efficacy of such antimicrobial surfaces has not been sufficiently investigated in hospitals. In this study, the antimicrobial activity of examination gloves with light-activated antimicrobial properties against Gram-positive microorganisms was investigated modelling real live conditions. METHOD:In a standardized experimental set-up with dry and realistic contamination, the antimicrobial properties of gloves claiming light dependent antimicrobial activity against Gram-positive organisms were tested in comparison with conventional examination gloves. All gloves were contaminated through a standardized activity of the test persons for construction with contaminated building blocks. For contamination suspensions of Enterococcus faecium ATCC 6057, Acinetobacter baumannii (outbreak strain), methicillin resistant Staphylococcus aureus ATCC 43300 or E. faecium (VRE) patient isolate were dried on the surfaces. After the standardized activity, the gloves were held for 10 min in the light present in the room (bright conditions) and the grade of contamination was determined subsequently by quantitative culture. In one experimental series gloves were held in a dark box after contamination as a control (dark conditions). RESULTS:The light intensity in all experiments under bright conditions was significantly above the limit value specified by the manufacturer for the activation of antimicrobial properties (> 500 lx). The mean values for experiments with antimicrobial active and non-active gloves were 955 and 935 lx, respectively. As claimed by the manufacture, the gloves showed no sufficient efficacy against A. baumannii under bright conditions. Against Gram-positive microorganisms such as E. faecium, E. faecium (VRE) and methicillin resistant S. aureus the gloves showed only very low antimicrobial activity with a reduction factor < 1 log10 even after 10 min in bright conditions. Interestingly, comparable results for experiments with A. baumannii and E. faecium were shown under dark conditions. CONCLUSION:The lack of activity of the active principle against Gram-negative microorganisms could be confirmed. The reduction factors of > 4 log10 within 5 min for Gram-positive microorganisms claimed for the product using a standard test procedure (ASTM D7907) could not be confirmed in a realistic experimental test set-up even after 10 min of light exposure. The effectiveness against Gram-positive microorganisms should be further investigated under realistic (dry) conditions, including patient care. At this stage, the use of supposedly antimicrobial gloves should not be recommended, as the belief in their efficacy may encourage the misuse of gloves.

Admission to a room previously occupied by patients carrying environmentally robust pathogens implies an increased risk of acquiring those pathogens. Therefore, 'No-touch' automated room disinfection systems, including devices based on UV-C irradiation, are discussed to improve terminal cleaning. It is still unclear if clinical isolates of relevant pathogens behave differently under UV-C irradiation compared to laboratory strains used in the approval process of disinfection procedures. In this study we analysed the susceptibility of well characterized clonally divergent vancomycin-resistant enterococci (VRE) strains, including a linezolid-resistant isolate, against UV-C radiation.Susceptibility against UV-C of ten clonally divergent clinical isolates of VRE was determined in comparison to the commonly used test organism Enterococcus hirae ATCC 10541. Ceramic tiles contaminated with 105 to 106 colony forming units/25 cm² of the different enterococci were positioned at a distance of 1.0 and 1.5 m and irradiated for 20 s, resulting in a UV-C dose of 50 and 22 mJ/cm², respectively. Reduction factors were calculated after quantitative culture of the bacteria recovered from treated and untreated surfaces.Susceptibility to UV-C varied considerably among the strains studied, with the mean value of the most robust strain being up to a power of ten lower compared to the most sensitive strain at both UV-C doses. The two most tolerant strains belonged to MLST sequence types ST80 and ST1283. The susceptibility of the laboratory strain E. hirae ATCC 10541 ranged between the most sensitive and most tolerant isolates for both irradiation doses. However, for UV-C dose of 22 mJ/cm², the reduction of the most tolerant isolate of ST1283 was statistically significantly lower compared to E. hirae ATCC 10541. The most susceptible strains belonged to the MLST sequence types ST117 and ST203.These results indicate that UV-C doses reported in the literature are sufficient for the reduction of commonly used reference strains of enterococci but could be insufficient for the reduction of tolerant patient VRE-isolates in a hospital setting. Therefore, for future studies, the most tolerant clinical isolates should be used to validate automated UV-C devices or longer exposure times should be expected to ensure efficacy in the real world.

Background The ongoing coronavirus disease 2019 pandemic significantly burdens hospitals and other healthcare facilities. Therefore, understanding the entry and transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is critical for effective prevention and preparedness measures. We performed surveillance and analysis of testing and transmission of SARS-CoV-2 infections in a tertiary-care hospital in Germany during the second and third pandemic waves in fall/winter 2020. Methods Between calendar week 41 in 2020 and calendar week 1 in 2021, 40%, of all positive patient and staff samples (284 total) were subjected to full-length viral genome sequencing. Clusters were defined based on similar genotypes indicating common sources of infection. We integrated phylogenetic, spatial, and temporal metadata to detect nosocomial infections and outbreaks, uncover transmission chains, and evaluate containment measures' effectiveness. Results Epidemiologic data and contact tracing readily recognize most healthcare-associated (HA) patient infections. However, sequencing data reveal that temporally preceding index cases and transmission routes can be missed using epidemiologic methods, resulting in delayed interventions and serially linked outbreaks being counted as independent events. While hospital-associated transmissions were significantly elevated at a moderate rate of community transmission during the second wave, systematic testing and high vaccination rates among staff have led to a substantial decrease in HA infections at the end of the second/beginning of the third wave despite high community transmissions. Conclusions While epidemiologic analysis is critical for immediate containment of HA SARS-CoV-2 outbreaks, integration of genomic surveillance revealed weaknesses in identifying staff contacts. Our study underscores the importance of high testing frequency and genomic surveillance to detect, contain and prevent SARS-CoV-2-associated infections in healthcare settings. A combination of genomic variant analysis and person-to-person contact tracing reconstructs entry of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) into a tertiary-care hospital from the community and identifies index patients and cryptic transmissions in hospital outbreaks. Vaccination and systematic polymerase chain reaction testing reduced hospital-associated SARS-CoV-2 infections.

Abstract Persistent somatic and neuropsychiatric symptoms have been frequently described in patients after infection with severe acute respiratory syndrome coronavirus 2 even after a benign clinical course of the acute infection during the early phases of the coronavirus severe acute respiratory syndrome coronavirus 2 pandemic and are part of Long COVID. The Omicron variant emerged in November 2021 and has rapidly become predominant due to its high infectivity and suboptimal vaccine cross-protection. The frequency of neuropsychiatric post-acute sequelae after infection with the severe acute respiratory syndrome coronavirus 2 Omicron and adequate vaccination status is not known. Here, we aimed to characterize post-acute symptoms in individuals with asymptomatic or mildly symptomatic breakthrough infection with severe acute respiratory syndrome coronavirus 2. These individuals had either proven infection with the Omicron variant (n = 157) or their infection occurred in 2022 where Omicron was the predominant variant of severe acute respiratory syndrome coronavirus 2 in Germany (n = 107). This monocentric cross-sectional study was conducted at the University Medical Center Hamburg-Eppendorf between 11 February 2022 and 11 April 2022. We employed questionnaires addressing self-reported somatic symptom burden (Somatic Symptom Scale 8) and neuropsychiatric symptoms including mood (Patient Health Questionnaire 2), anxiety (Generalized Anxiety Disorder 7), attention (Mindful Attention Awareness Scale) and fatigue (Fatigue Assessment Scale) in a cohort of hospital workers. Scores were compared between 175 individuals less than 4 weeks after positive testing for severe acute respiratory syndrome coronavirus 2, 88 individuals more than 4 weeks after positive testing and 87 severe acute respiratory syndrome coronavirus 2 uninfected controls. The majority (n = 313; 89.5%) of included individuals were vaccinated at least three times. After recovery from infection, no significant differences in scores assessing neuropsychiatric and somatic symptoms were detected between the three groups (severe acute respiratory syndrome coronavirus 2 uninfected controls, individuals less and more than 4 weeks after positive testing) independent of age, sex, preconditions and vaccination status. In addition, self-reported symptom burden did not significantly correlate with the number of vaccinations against severe acute respiratory syndrome coronavirus 2, time from recovery or the number of infections. Notably, in all three groups, the mean scores for each item of our questionnaire lay below the pathological threshold. Our data show that persistent neuropsychiatric and somatic symptoms after recovery from severe acute respiratory syndrome coronavirus 2 infection in fully vaccinated hospital workers do not occur more frequently than that in uninfected individuals. This will guide healthcare professionals in the clinical management of patients after recovery from breakthrough infections with severe acute respiratory syndrome coronavirus 2.

BACKGROUND:Worldwide observations revealed increased frequencies of multi-resistant Enterobacterales and resistance genes in hospital wastewater compared to any other type of wastewater. Despite the description of clonal lineages possibly adapted to hospital wastewater, little is known about long term persistence as well as evolution of these lineages. METHODS:In this study, wastewater isolates of different Enterobacterales species from a tertiary care hospital were investigated with 2.5 years distance. Whole Genome Sequencing (WGS) and resistance gene identification were performed for E. coli, C. freundii, S. marcescens, K. pneumoniae, K. oxytoca, and E. cloacae isolates (n = 59), isolated in 2022 and compared with strains isolated from the same wastewater pipeline in 2019 (n = 240). RESULTS:Individual clonal lineages with highly related isolates could be identified in all species identified more than once in 2022 that appear to persist in the wastewater drainage. A common motif of all persistent clonal lineages was the carriage of mobile genetic elements encoding carbapenemase genes with hints for horizontal gene transfer in persistent clones in this environment observed over the 2.5-year period. Multiple plasmid replicons could be detected in both years. In 2022 isolates blaVIM-1 replaced blaOXA-48 as the most common carbapenemase gene compared to 2019. Interestingly, despite a similar abundance of carbapenemase genes (>80% of all isolates) at both time points genes encoding extended spectrum β-lactamases decreased over time. CONCLUSIONS:This data indicates that hospital wastewater continuously releases genes encoding carbapenemases to the urban wastewater system. The evolution of the resident clones as well as the reasons for the selection advantage in this specific ecological niche needs to be further investigated in the future.

BACKGROUND:Various assay methods have been developed to study antimicrobial activity based on contamination of surfaces with different amounts of liquid bacterial suspensions. Since surfaces with frequent hand contact are typically touched in a dry state in clinical settings, these tests may be inappropriate at assessing effectiveness to reduce pathogen transmission. AIM:To investigate a surface previously confirmed to display antimicrobial activity even after drying of small volumes of bacterial suspension (Egger antimicrobial surfaces: EAS) under conditions modelling dry contamination using a touch-transfer method. METHODS:EAS, an antimicrobial copper alloy, as well as a negative control were examined to assess interlaboratory test reproducibility. FINDINGS:Significantly fewer bacteria on EAS after touch transfer and some differences in the touch transmission were detected between the two laboratories. However, an identical assessment of effectiveness for EAS came from both laboratories. Interestingly, despite previously detected antimicrobial efficacy of EAS and the antimicrobial copper alloy after liquid contamination, insufficient activity was observed under dry conditions during a contact time of 4 h by both laboratories. Experiments under standardized air humidity in one laboratory revealed at least for copper a strong influence of humidity on antimicrobial activity. These data indicate that procedures involving contamination of surfaces with organisms suspended in liquids are not directly comparable to dry contamination. CONCLUSION:Since, in the real world of a hospital, organisms are typically transferred between dry surfaces, further standardization of the touch-transfer method is worthwhile for a better understanding of the efficacy of such surfaces.

Regulations for measures to protect against SARS-CoV-2 transmission vary widely around the world, with very strict regulations in Germany where respirators (filtering face piece FFP2 or comparable) are often mandatory. The efficiency of respirators, however, depends essentially on the tight facial fit avoiding the bypass of contaminated air via gaps between mask and wearer's face. The facial fit can be verified in a fit test. The aim of this review was to describe the quantitative fit test results depending on the respirator designs. A literature search revealed 29 suitable studies. Of all respirators with circumferential head straps, three-panel folded dome-shaped respirators showed the best fit (80.8% of 4625 fit tests passed), followed by rigid-dome-shaped respirators (72.4% of 8234 fit tests passed), duckbill-shaped respirators (31.6% of 2120 fit tests passed), and coffee-filter-shaped respirators (30.9% of 3392 fit tests passed). Respirators with ear loops showed very poor tight fit (3.6% of 222 fit tests passed). In four randomized control trials, single-use respirators were not shown to be superior to surgical masks for the prevention of laboratory-confirmed viral respiratory infections, even when adjusted with a fit test. Therefore, we consider the mandatory use of respirators to be disproportionate and not supported by evidence. Further evidence should be generated, in which scenarios respirators might provide an effective benefit as part of occupational health and safety. For situations with confirmed benefits, only high-quality disposable respirators with head straps or respiratory protective equipment of higher protective levels should be used.

Pigmentation, catalase activity and biofilm formation are virulence factors that cause resistance of Staphylococcus aureus to environmental stress factors including disinfectants. In recent years, automatic UV-C room disinfection gained greater importance in enhanced disinfection procedures to improve disinfection success in hospitals. In this study, we evaluated the effect of naturally occurring variations in the expression of virulence factors in clinical S. aureus isolates on tolerance against UV-C radiation. Quantification of staphyloxanthin expression, catalase activity and biofilm formation for nine genetically different clinical S. aureus isolates as well as reference strain S. aureus ATCC 6538 were performed using methanol extraction, a visual approach assay and a biofilm assay, respectively. Log(10) reduction values (LRV) were determined after irradiation of artificially contaminated ceramic tiles with 50 and 22 mJ/cm(2) UV-C using a commercial UV-C disinfection robot. A wide variety of virulence factor expression was observed, indicating differential regulation of global regulatory networks. However, no direct correlation with the strength of expression with UV-C tolerance was observed for either staphyloxanthin expression, catalase activity or biofilm formation. All isolates were effectively reduced with LRVs of 4.75 to 5.94. UV-C disinfection seems therefore effective against a wide spectrum of S. aureus strains independent of occurring variations in the expression of the investigated virulence factors. Due to only minor differences, the results of frequently used reference strains seem to be representative also for clinical isolates in S. aureus.

Background: The efficacy of ultraviolet C (UV -C) radiation against a broad spectrum of micro-organisms has been demonstrated in several studies, but differences in the specific doses and the extent of microbial reduction were found. Furthermore, the conditions of laboratory tests differ greatly from reality, such that efficacy achieved in tests may not necessarily be assumed in reality. Consequently, it is important to investigate the effectiveness of UV-C in representative field trials. The aim was therefore to develop and establish a field test to evaluate automatic UV-C in comparison to manual disinfection.Methods: Before and after disinfection, samples were repeatedly collected from naturally highly contaminated surfaces using the swab technique to obtain representative data sets for disinfected and non-disinfected surfaces. Subsequently, the log reduction values (LRV) and the disinfection success were evaluated for UV-C radiation and full compliant manual disinfection using alcohol-based wipes. Results: Surfaces that are naturally contaminated with bacteria on a regular and nearly uniform basis have been identified as particularly suitable for field testing. Mean contamination was reduced from 23.3 to 1.98 cfu/cm2 (LRV 0.9) and 29.7 to 0.26 cfu/cm2 (LRV 1.2) for UV-C and manual disinfection, respectively. UV-C disinfection achieved 75.5% successful disinfected surfaces, whereas manual disinfection showed 98.1%.Conclusions: Full compliant manual disinfection showed slightly higher LRVs and disinfection success than automatic UV-C disinfection. Successful, operator-independent UV-C disinfection still has the potential to improve disinfection performance in addition to manual disinfection.& COPY; 2023 The Healthcare Infection Society. Published by Elsevier Ltd. All rights reserved.

SARS-CoV-2 RNA is frequently identified in patient rooms and it was speculated that the viral load quantified by PCR might correlate with infectivity of surfaces. To evaluate Ct values for the prediction of infectivity, we investigated contaminated surfaces and Ct-value changes after disinfection. Viral RNA was detected on 37 of 143 investigated surfaces of an ICU. However, virus isolation failed for surfaces with a high viral RNA load. Also, SARS-CoV-2 could not be cultivated from surfaces artificially contaminated with patient specimens. In order to evaluate the significance of Ct values more precisely, we used surrogate enveloped bacteriophage Φ6. A strong reduction in Φ6 was achieved by three different disinfection methods. Despite a strong reduction in viability almost no change in the Ct values was observed for UV-C and alcoholic surface disinfectant. Disinfection using ozone resulted in a lack of Φ6 recovery as well as a detectable shift in Ct values indicating strong degradation of the viral RNA. The observed lack of significant effects on the detectable viral RNA after effective disinfection suggest that quantitative PCR is not suitable for predicting the infectivity of SARS-CoV-2 on inanimate surfaces. Ct values should therefore not be considered as markers for infectivity in this context.

The potential impact of music-making on air quality around musicians was inferred at the outset of the SARS-CoV-2 pandemic from measurements on individual musical instruments and from theoretical considerations. However, it is unclear to what extent playing together in an orchestra under optimal ventilation conditions really increases infection risks for individual musicians. In this study, changes in indoor air quality were assessed by measuring common parameters, i.e., temperature, relative humidity, and carbon dioxide, along with particle counting and determining the presence of airborne pharyngeal bacteria under different seating arrangements. The study was conducted in cooperation with a professional orchestra on a stage ventilated by high volume displacement ventilation. Even with a full line-up, the particle load was only slightly influenced by the presence of the musicians on stage. At the same time, however, a clear increase in pharyngeal flora could be measured in front of individual instrument groups, but independent of seat spacing. Simultaneous measurement of various air parameters and, above all, the determination of relevant indicator bacteria in the air, enables site-specific risk assessment and safe music-making even during a pandemic.

Background: The immunogenicity of different COVID-19 vaccine regimens and combinations in naïve and convalescent individuals has not been formally tested in controlled studies, and real-life observational studies are scarce. Methods: We assessed the SARS-CoV-2 infection and COVID-19 vaccination-induced immunity of 697 hospital workers at the University Medical Center Hamburg-Eppendorf between 17 and 31 January 2022. Results: The overall prevalence of anti-NC-SARS-CoV-2 antibodies indicating prior infection was 9.8% (n = 68) and thus lower than the seroprevalence in the general population. All vaccinated individuals had detectable anti-S1-RBD-SARS-CoV-2 antibodies (median AU/mL [IQR]: 13,891 [8505–23,543]), indicating strong protection against severe COVID-19. Individuals who received three COVID-19 vaccine doses (median AU/mL [IQR]: 13,856 [8635–22,705]) and those who resolved a prior SARS-CoV-2 infection and had received two COVID-19 vaccine doses (median AU/mL [IQR] 13,409 [6934–25,000]) exhibited the strongest humoral immune responses. Conclusions: The current study indicates that three exposures to the viral spike protein by either SARS-CoV-2 infection or COVID-19 vaccination are necessary to elicit particularly strong humoral immune responses, which supports current vaccination recommendations.

The infection control strategies to prevent transmission of SARS-CoV-2 in healthcare settings vary between European countries. In a recent proposal published on 3rd August 2022, the German Federal Ministry of Health intends to change the current version of the infection control act regarding COVID-19 [[1]Bundesministerium für GesundheitPandemievorsorge für Herbst und Winter: neuer rechtlicher Rahmen im Infektionsschutzgesetz – Bundesgesundheitsministerium.2022https://www.bundesgesundheitsministerium.de/presse/pressemitteilungen/fortentwicklung-infektionsschutzgesetzes-ifsg.htmlGoogle Scholar,[2]Bundesministerium für GesundheitCorona: gut vorbereitet in den Herbst – Bundesregierung.2022https://www.bundesregierung.de/breg-de/suche/infektionsschutzgesetz-2068856Google Scholar]. The new measures are expected to be valid from 1st October 2022. Filtering facepiece respirators of the FFP2 type (equivalent to N95 respirators) are the key component of the new concept. FFP2 respirators and negative COVID-19 tests will then be required for access to hospitals and nursing homes as well as for employees in outpatient nursing services unless the person provides evidence for an up-to-date COVID-19 vaccination or has recovered from COVID-19 within the last three months. This proposal, however, lacks proportionality and does not take into account relevant recent findings, especially for the healthcare sector. First, medical masks and FFP2 respirators offer a similar level of protection in preventing laboratory-confirmed viral infection and respiratory illness including coronavirus specifically in healthcare workers (HCWs) [[3]Bartoszko J.J. Farooqi M.A.M. Alhazzani W. Loeb M. Medical masks vs N95 respirators for preventing COVID-19 in healthcare workers: a systematic review and meta-analysis of randomized trials.Influenza Other Respir Viruses. 2020; 14: 365-373Crossref PubMed Scopus (275) Google Scholar] although the filtration efficacy of the respirator material is higher [[4]Ju J.T.J. Boisvert L.N. Zuo Y.Y. Face masks against COVID-19: standards, efficacy, testing and decontamination methods.Adv Colloid Interface Sci. 2021; 292102435Crossref PubMed Scopus (33) Google Scholar]. A randomized controlled trial comparing respirators and medical masks for the prevention of influenza, which has comparable transmission routes, showed no advantages for respirators in the protection of HCWs [[5]Radonovich L.J. Simberkoff M.S. Bessesen M.T. Brown A.C. Cummings D.A.T. Gaydos C.A. et al.N95 respirators vs medical masks for preventing influenza among health care personnel: a randomized clinical trial.JAMA. 2019; 322: 824-833Crossref PubMed Scopus (290) Google Scholar]. Second, universal masking or respirator use alone is not a panacea in a hospital. A mask or respirator alone will not protect providers caring for a patient with active COVID-19 if it is not accompanied by meticulous hand hygiene and additional personal protective equipment such as eye protection or gowns [[6]Klompas M. Morris C.A. Sinclair J. Pearson M. Shenoy E.S. Universal masking in hospitals in the COVID-19 era.N Engl J Med. 2020; 382: e63Crossref PubMed Scopus (172) Google Scholar]. A respirator alone will also not prevent HCWs with early COVID-19 from contaminating their hands and potentially spreading the virus to patients and colleagues [[6]Klompas M. Morris C.A. Sinclair J. Pearson M. Shenoy E.S. Universal masking in hospitals in the COVID-19 era.N Engl J Med. 2020; 382: e63Crossref PubMed Scopus (172) Google Scholar]. In addition, the release of particles into the environment is dependent on facial movement and flow velocity of exhaled air (quiet breathing, talking, coughing) and can be significantly higher with a respirator compared with a medical mask [[7]Asadi S. Cappa C.D. Barreda S. Wexler A.S. Bouvier N.M. Ristenpart W.D. Efficacy of masks and face coverings in controlling outward aerosol particle emission from expiratory activities.Sci Rep. 2020; 1015665Crossref Scopus (174) Google Scholar]. Third, the protection of persons wearing respirators largely depends on the fitting. Fit failure rates of N95 respirators have been reported to be between 60% and 90%, especially in extended use ≥1 h [[8]Jung J. Kim J. Yang H. Lim Y.J. Kwak S.H. Hong M.J. et al.Fit-failure rate associated with simulated reuse and extended use of N95 respirators assessed by a quantitative fit test.Infect Control Hosp Epidemiol. 2021; 42: 1313-1317Crossref PubMed Scopus (1) Google Scholar]. KF94 respirators (equivalent to FFP2/N95 respirators) have been described with rather poor tight fittings, especially for ear-loop-type respirators, such that the face seal was not maintained with movement providing inadequate respiratory protection [[9]Yang H.J. Yoon H. Kang S.Y. Lee G. Park J.E. Kim T. et al.Respiratory protection effect of ear-loop-type KF94 masks according to the wearing method in COVID-19 pandemic: a randomized, open-label study.J Korean Med Sci. 2021; 36: e209Crossref PubMed Google Scholar]. Mandatory FFP2 respirators in healthcare may even result in a shortage of products with circumferential headbands such that the ear-loop-type respirators may have to be used. Fourth, FFP2 respirators have been shown to significantly increase self-perceived dyspnoea after only a 6-min walk [[10]Cabanillas-Barea S. Rodríguez-Sanz J. Carrasco-Uribarren A. López-De-celis C. González-Rueda V. Zegarra-Chávez D. et al.Effects of using the surgical mask and FFP2 during the 6-min walking test. A randomized controlled trial.Int J Environ Res Public Health. 2021; 1812420Crossref Scopus (5) Google Scholar]. Fifth, the expectable protective effect depends on the type of clinical situation. FFP2 respirators revealed a significantly higher protective effect for HCWs with frequent (>20 patients) COVID-19 exposure [[11]Haller S. Güsewell S. Egger T. Scanferla G. Thoma R. Leal-Neto O.B. et al.Impact of respirator versus surgical masks on SARS-CoV-2 acquisition in healthcare workers: a prospective multicentre cohort.Antimicrob Resist Infect Control. 2022; 11: 27Crossref PubMed Scopus (5) Google Scholar]. N95 respirators significantly reduced the risk for HCWs to acquire COVID-19 when working under aerosol conditions or in a designated COVID-19 area of the hospital [[12]Chano T. Morita S. Suzuki T. Yamashita T. Fujimura H. Yuri T. et al.Serology suggests adequate safety measures to protect healthcare workers from COVID-19 in Shiga Prefecture, Japan.PLoS One. 2022; 17e0270334Crossref PubMed Scopus (2) Google Scholar]. We think that a general FFP2 respirator mandate for HCWs cannot be scientifically justified and is the wrong way to go. In German hospitals, an interdisciplinary commission (infection prevention commission) is mandatory taking into account both infection control and occupational health aspects, which by law has the function of determining infection prevention measures on the basis of the risk profile of the respective facility. The members know the vulnerability of their patients very well and should decide locally on suitable and effective infection control measures. All authors conceived of the idea to write the letter. G.K. prepared the first draft, the other authors added relevant aspects and citations and thereby contributed to various aspects of the text. J.K.K., M.E., P.W. and G.K. have no conflicts of interest to declare. W.P. has received honoraria for presentation from 3M. The views expressed here are those of the authors and do not necessarily reflect those of their universities. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.