Background: Although many studies have examined the effects of temperature or humidity on influenza, few studies investigated other meteorological factors, let alone their joint effects. This study aimed to investigate the joint effects of meteorological factors on influenza in China and identified main factors contributing to the joint effect. Methods: Influenza cases data during 2015-2019 in 324 prefectures of China were collected from the Chinese Center for Disease Control and Prevention. Meteorological data were obtained from the Land-ERA5 dataset of the European Centre for Medium-Range Weather Forecasts. We adopted a two-stage analysis strategy. In the first stage, distributed hysteresis nonlinear model (DLNM) was used to study the exposure response relationship between temperature, relative humidity, wind speed, and atmospheric pressure and influenza, and in the second stage, meta-analysis was used to obtain the exposure response relationship at the national level. Then, a quantile gcomputation (qgcomp) model was employed to assess the joint effects of mixture exposure to the four meteorological factors on influenza. Results: There were 5,093,710 influenza cases included in the study. There were U-shaped relationships between temperature, relative humidity, atmospheric pressure and influenza, while wind speed showed a negative effect on influenza. It was also a U-shaped association of mixture exposure to all the four meteorological factors with influenza. The highest risk was observed at the fourth quantile of the mixture exposure (RR 1.21; 95 % CI[1.11-1.32]) in total population, and temperature was the most important contributor (54.15 %) to the joint effect, followed by atmospheric pressure (24.46 %), wind speed (16.52 %) and relative humidity (4.87 %). Conclusion: The study found that mixture exposure to meteorological factors associated with influenza, and temperature contributed most to the combined effect.

Background: Influenza is a major health threat to the elderly in China. Despite this, influenza vaccination rates still remain low and vary across regions that have different funding policies. In this study, we compare the vaccination status and influencing factors among older adults under the free, partial reimbursement, and self-paid vaccination strategies. Methods: Three cities with free, partial reimbursement, and self-paid influenza vaccination policies were selected. A cross-sectional, anonymous survey was then conducted. A total of 2265 elderly individuals aged 60 years and above were recruited using probability proportionate to size sampling. A standardized questionnaire was used during face-to-face interviews to collect data regarding the influenza vaccination status and influencing factors. The statistical analyses included chi-square tests, a multivariate logistic regression, and random forest models. Results: Among the 2265 participants (free policy region: n = 426; partial reimbursement region: n = 633; self-paid region: n = 1206), vaccination rates during the 2023–2024 season were significantly higher in the free policy region (53.29%) than in the partial reimbursement (20.85%) and self-paid (13.60%) regions (p < 0.001). The intention to vaccinate for the 2024–2025 season was also highest in the free policy region (68.78%), followed by partial reimbursement (47.71%) and self-paid (37.15%) regions (p < 0.001). This result demonstrated the same trend as the vaccination behavior. Cues to action (e.g., healthcare worker or family member recommendations) positively influenced vaccinations across all of the regions. In the self-paid region, perceived barriers, such as vaccine cost and side effect concerns, significantly reduced both behaviors and the next-season intention to vaccinate. Healthcare worker recommendations were key positive factors, while misconceptions and costs were major barriers to vaccination. Conclusions: Vaccination rates varied significantly across regions with different influenza vaccine subsidy policies. The free policy region demonstrated the highest coverage rate, while the self-paid region exhibited the lowest, suggesting that financial policies are a key determinant of vaccination uptake. Furthermore, free vaccination policies were associated with improved influenza vaccine knowledge among the elderly. Analysis of other influencing factors revealed that healthcare workers’ recommendations played a crucial role across all policy regions, though their impact on current-season vaccination behavior and next-season vaccination intention differed by subsidy context. Further studies are needed to explore the best approaches for optimizing region-specific subsidy strategies for promoting influenza vaccination among the elderly in China.

Influenza imposes a significant disease burden on society and individuals annually, and influenza vaccination is considered a significant public health measure to prevent influenza and reduce influenza-related severe disease and death. The low influenza vaccination rate in China is partly due to certain factors affecting the willingness and behavior of individuals to receive them. Scientific research and targeted interventions on these factors can effectively improve the vaccination situation. Commonly used individual-level theoretical models for influenza vaccination behavior include the health belief model, protection motivation theory, and theory of planned behavior. This study reviews theoretical models commonly employed in researching influenza vaccination willingness and behavior. An overview of these practical applications and challenges models is presented to provide references for relevant research and intervention programs in China.

Objective: To understand the performance of 2019-nCoV nucleic acid detection in screening of contacts of COVID-19 cases in same flights and provide evidence for the effective screening of persons at high risk for the infection in domestic flights. Methods: The information of passengers who took same domestic flights with COVID-19 cases in China from April 1, 2020 to April 30, 2022 were retrospectively collected,and χ2 test was used to analyze positive nucleic acid detection rates in the passengers in different times before the onsets of the index cases, in different seat rows and in epidemic periods of different 2019-nCoV variants. Results: During the study period, a total of 433 index cases were identified among 23 548 passengers in 370 flights. Subsequently, 72 positive cases of 2019-nCoV nucleic acid were detected in the passengers, in whom 57 were accompanying persons of the index cases. Further analysis of the another 15 passengers who tested positive for the nucleic acid showed that 86.67% of them had onsets or positive detections within 3 days after the diagnosis of the index cases, and the boarding times were all within 4 days before the onsets of the index cases. The positive detection rate in the passengers who seated in first three rows before and after the index cases was 0.15% (95%CI: 0.08%-0.27%), significantly higher than in the passengers in other rows (0.04%, 95%CI: 0.02%-0.10%, P=0.007),and there was no significant difference in the positive detection rate among the passengers in each of the 3 rows before and after the index cases (P=0.577). No significant differences were found in the positive detection rate in the passengers, except the accompanying persons, among the epidemics caused by different 2019-nCoV variants (P=0.565). During the Omicron epidemic period, all the positive detections in the passengers, except the accompanying persons, were within 3 days before the onset of the index cases. Conclusions: The screening test of 2019-nCoV nucleic acid can be conducted in the passengers took the same flights within 4 days before the onsets of the index cases on board. Passengers who seated within 3 rows from the index cases can considered as the close contacts at high risk for 2019-nCoV, for whom screening should be conducted first and special managements are needed. The passengers in other rows can be classified as general risk persons for screening and management.

Influenza is an acute respiratory infectious disease caused by influenza virus. Pregnancy is associated with physiologic and immunological changes that may increase the risk for influenza virus infection and influenza-related complications. Influenza vaccination is the most effective way to prevent influenza virus infection. WHO and many countries have classified pregnant women as a priority population for influenza vaccination, however, there are still many challenges for promoting influenza vaccination in pregnant women in China, influenza vaccination coverage in pregnant women remains low and some influenza vaccine package inserts list pregnancy as an absolute contraindication. In this paper, we summarize the research progress in the effects of influenza infection and influenza vaccination during pregnancy both at home and abroad, then discuss the strategies to promote influenza vaccination in pregnancy for the purpose of providing reference for the related research and policy development in China.

Background Mild hand, foot and mouth disease (HFMD) cases make up a relatively high proportion of HFMD while have often been overlooked. This study aimed to investigate the epidemiological and etiological characteristics of mild HFMD in Nanjing. Methods Data on mild HFMD cases, during 2010–2019 in Nanjing, were collected from the China Information System for Disease Control and Prevention. This study mainly focused on mild cases aged < 7 years. Descriptive analysis was used to summarize epidemiological and etiological characteristics of mild cases. Flexible spatial scan statistic was used to detect spatial clusters of mild cases. Results A total of 175,339 mild cases aged < 7 years were reported, accounting for 94.4% of all mild cases. There was a higher average annual incidence of mild HFMD in children aged < 7 years (4,428 cases/100,000) compared with children aged ≥ 7 years (14 cases/100,000, P < 0.001), and especially children aged 1-year-old (7,908 cases/100,000). Mild cases showed semi-annual peaks of activity, including a major peak (April to July) and a minor peak (September to November). The average annual incidence was higher in males (5,040 cases/100,000) than females (3,755 cases/100,000). Based on the cumulative reported cases, the most likely cluster was detected, including Yuhuatai District, Jiangning District, Jiangbei new Area, and Pukou District. The annual distribution of enterovirus serotypes showed a significant difference. During 2010–2016, Enterovirus 71 (EV71), Coxsackievirus A16 (Cox A16), and other non-EV71/Cox A16 EVs, accounted for 29.1%, 34.6%, 36.3% of all the enterovirus test positive cases, respectively. Moreover, during 2017–2019, Cox A6, Cox A16, EV71, and other non-EV71/Cox A16/Cox A6 EVs, accounted for 47.3%, 32.5%, 10.7%, 9.5%, respectively. Conclusions Children under 7 years old are at higher risk of mild HFMD. Regions with high risk are mainly concentrated in the areas surrounding central urban areas. Cox A16 and Cox A6 became the dominant serotypes and they alternated or were co-epidemic. Our findings could provide valuable information for improving the regional surveillance, prevention and control strategies of HFMD.

Objective: To investigate the policies and coverage of influenza vaccine during the influenza epidemic seasons of 2020-2021 and 2021-2022 in China. Methods: The national influenza vaccination policy and vaccination rate were investigated in counties and districts and described in the two epidemic seasons. Results: In the epidemic seasons of 2020-2021 and 2021-2022, the vaccination coverage of influenza in China was 3.16% and 2.47%, respectively. The free vaccination policy had the highest vaccination coverage (51.75% and 38.32%), followed by the medical insurance reimbursement policy (9.74% and 7.36%). During the epidemic season of 2021-2022, the number of counties and districts implementing the free vaccination policy in China decreased 61 compared with the previous year, but the number of people covered increased by 51.29%. However, the vaccination coverage of the vast population decreased significantly, with the medical staff (75.69% and 40.15% for two epidemic seasons), preschool children (58.86% and 26.15%), and the elderly (45.71% and 32.94%). During the epidemic season of 2021-2022, the number of counties and districts implementing the medical insurance reimbursement policy increased by 6 compared with the previous year, and the number of people covered increased by 11.12%, but the vaccination coverage decreased. Conclusion: The influenza vaccination rate in China is low, and the implementation of cost preferential policy can greatly improve the influenza vaccination rate.

目的 调查南京市一起幼儿园水痘暴发疫情的危险因素和评估水痘减毒活疫苗（VarV）的免疫效果。方法 确定病例定义并完成病例搜索，收集病例基本信息、临床记录、流行病学史、水痘免疫史等资料，描述病例三间分布特征和罹患率差异。收集罹患率较高班级全部幼儿的水痘免疫史和水痘患病史，采用回顾性队列研究方法分析接种与未接种疫苗的幼儿间罹患率差异，评估疫苗免疫效果以及不同接种时间间隔对疫苗免疫效果的影响。结果 共收集61例水痘病例，幼儿罹患率10.87%（59/543）显著高于教职工2.94%（2/68）（χ~2=4.22,P=0.040）。首发病例为一名教职工，发病后仍在岗工作，未被学校常规健康监测发现，也未进行主动报告；其请病假后，校方未采取干预措施。疫情持续2个月，累计发生5代病例，代间距中位数15 d。不同班级间罹患率差异有统计学意义（χ~2=256.98,P＜0.001）。突破性病例8例（13.11%）均仅接种1剂VarV，接种VarV至发病的时间间隔中位数4.11年。结果显示，疫苗保护效果为65%（95%置信区间：24%～84%）;1剂次疫苗接种年限＞3年其保护效果下降。结论 本次报道为一起首发病例为教职工的幼儿园水痘暴发疫情。未及时发现和隔离病例、教室布局拥挤、疫苗接种覆盖率低及1剂次疫苗接种年限长是疫情发生的可能危险因素。

Objective:To analyze the characteristics of influenza vaccines lot release in China from 2007 to 2020, so as to provide references for the research, development and vaccines production, and for influenza outbreak prevention and control in China.Methods:The targeted lot release data of biological products by end of February 2021 were downloaded from the website of National Institutes for Food and Drug Control (NIFDC). Relevant lot release characteristics of influenza vaccines were analyzed eventually. To quantify the possible trend of influenza vaccines lot release volumes, a Joinpoint regression model analysis was conducted.Results:The Joinpoint regression model showed that in the influenza seasons from 2007/08 to 2009/10, the annual percent change (APC) of influenza vaccines lot release volumes was 67.3% (95% CI: 11.3% - 151.5%), indicating a trend of increasing in influenza vaccines lot release volumes. In the influenza seasons from 2009/10 to 2018/19, the APC was -14.8% (95% CI: - 18.5% - -11.0%), showing a trend of decreasing. In the influenza seasons from 2018/19 to 2020/21, the APC was 72.3% (95% CI: 14.6% - 158.9%), showing the trend of increasing. Over all, the average annual percent change (AAPC) in the influenza seasons from 2006/07 to 2020/21 was 5.3% (95% CI: -2.3% - 13.5%). There was no statistically significant difference ( P>0.05) in the influenza vaccines lot release volumes. The number of influenza vaccine manufacturers reduced and tended to maintain. Trivalent split influenza vaccines were the dominant influenza vaccine in China, and quadrivalent split influenza vaccines and trivalent live attenuated influenza vaccine were approved in 2018 and 2020 separately. At present, trivalent split influenza vaccines is the only product for children aged 6 months to 3 years, and the lot release volume is much lower than that for persons aged 3 years and older (29.1% vs 70.9%). More than 90% of influenza vaccines can be approved and released before end of October. Conclusions:The decline trend of influenza vaccine lot release volumes and the manufacturers has changed in recent years, and the types of influenza vaccines were gradually increasing. It is necessary to increase influenza vaccines for children aged 6 months to 3 years and develop other novel influenza vaccines in the future.

Influenza endangers human health but can be prevented in part by vaccination. Assessing influenza vaccine effectiveness (VE) provides scientific evidence for developing influenza vaccination policy. We conducted a systematic review and meta-analysis of studies that evaluated influenza VE in mainland China. We searched six relevant databases as of 30 August 2019 to identify studies and used Review Manager 5.3 software to analyze the included studies. The Newcastle–Ottawa scale was used to assess the risk of publication bias. We identified 1408 publications, and after removing duplicates and screening full texts, we included 21 studies in the analyses. Studies were conducted in Beijing, Guangzhou, Suzhou, and Zhejiang province from the 2010/11 influenza season through the 2017/18 influenza season. Overall influenza VE for laboratory confirmed influenza was 36% (95% CI: 25–46%). In the subgroup analysis, VE was 45% (95% CI: 18–64%) for children 6–35 months who received one dose of influenza vaccine, and 57% (95% CI: 50–64%) who received two doses. VE was 47% (95% CI: 39–54%) for children 6 months to 8 years, and 18% (95% CI: 0–33%) for adults ≥60 years. For inpatients, VE was 21% (95% CI: −11–44%). We conclude that influenza vaccines that were used in mainland China had a moderate effectiveness, with VE being higher among children than the elderly. Influenza VE should be continuously monitored in mainland China to provide evidence for policy making and improving uptake of the influenza vaccine.

BACKGROUND:The relative contributions of asymptomatic, presymptomatic, and symptomatic transmission of severe acute respiratory syndrome coronavirus 2 have not been clearly measured, although control measures may differ in response to the risk of spread posed by different types of cases. METHODS:We collected detailed information on transmission events and symptom status based on laboratory-confirmed patient data and contact tracing data from 4 provinces and 1 municipality in China. We estimated the variation in risk of transmission over time and the severity of secondary infections by symptomatic status of the infector. RESULTS:There were 393 symptomatic index cases with 3136 close contacts and 185 asymptomatic index cases with 1078 close contacts included in the study. The secondary attack rates among close contacts of symptomatic and asymptomatic index cases were 4.1% (128 of 3136) and 1.1% (12 of 1078), respectively, corresponding to a higher transmission risk from symptomatic cases than from asymptomatic cases (odds ratio, 3.79; 95% confidence interval, 2.06-6.95). Approximately 25% (32 of 128) and 50% (6 of 12) of the infected close contacts were asymptomatic from symptomatic and asymptomatic index cases, respectively, while more than one third (38%) of the infections in the close contacts of symptomatic cases were attributable to exposure to the index cases before symptom onset. CONCLUSIONS:Asymptomatic and presymptomatic transmissions play an important role in spreading infection, although asymptomatic cases pose a lower risk of transmission than symptomatic cases. Early case detection and effective test-and-trace measures are important to reduce transmission.

COVID-19 is an emerging infectious disease caused by SARS-CoV-2. After the infection of the virus, the host immune system is stimulated to produce multifarious specific antibodies to decrease or eliminate effects of the pathogen. Study of the specific antibodies dynamic characteristics in patients with COVID-19 is very important for the understanding and diagnosis of the disease, research and development of vaccine, and planning of prevention and control strategy. This paper reviews and summarizes the domestic and oversea research on dynamic characteristics of specific antibodies of COVID-19 patients, including the antibody producing, duration and level, and its possible influencing factors in order to improve the understanding of the immunological characteristics of COVID-19.

Objective: To analyze the incidence of acute respiratory infection (ARI) and related healthcare seeking behaviors in population in the period of COVID-19 epidemic in China. Methods: According to the province specific cumulative incidence rates of COVID-19 reported as of March 31, 2020, the low, medium and high-risk areas were classified. In these areas, a stratified two stage cluster random sampling method was used to select participants for face-to-face questionnaire surveys. Data on the incidence of ARI and related healthcare seeking behaviors in community residents during COVID-19 epidemic period were collected to calculate the attack rate of ARI and related healthcare seeking rate. Logistic regression method was used to explore the influencing factors for ARI incidence and healthcare seeking behavior. Results: A total of 34 857 community residents were surveyed, in whom 647 (1.9%) reported that they had ARI symptoms during the COVID-19 epidemic period, and 241 (37.2%) had healthcare seeking behaviors. In terms of the incidence of COVID-19-related ARI, in high-risk area, the risk of COVID-19-related ARI was 1.36 times (95%CI: 1.12-1.65) than that in low-risk area; among different age groups, the risk of COVID-19-related ARI in age groups 20-39 years, ≥60 years was 1.80 times (95%CI: 1.29-2.59) and 1.63 times (95%CI: 1.14-2.40) than that in age group 1-9 years; the risk of COVID-19-related ARI in people with underlying diseases was 1.53 times (95%CI: 1.23-1.89) than that in those without underlying diseases; the risk of COVID-19-related ARI in people with contacts with confirmed cases of COVID-19 and people with fever or respiratory symptoms was 1.53 times (95%CI: 1.01-2.27) and 6.60 times (95%CI: 5.05-8.53) than those in people without these contacts. The healthcare seeking rate in COVID-19-related ARI patients with exposures to those with fever or respiratory symptoms was 1.68 times (95%CI: 1.05-2.70) than that in such patients without the exposures. Conclusions: The attack rate of COVID-19-related ARI was affected by the local epidemic level of COVID-19, and in high-risk area, the attack rate of COVID-19-related ARI was also high. The healthcare seeking rate in patients with COVID-19-related ARI was low. Therefore, it is necessary to encourage the healthcare seeking in people with ARI in COVID-19 pandemic period.

目的 通过开展线上问卷调查,了解公众对新型冠状病毒肺炎重要防控知识的知晓情况,以更好地开展后续宣传教育工作.方法 使用问卷星生成问卷,并通过中国疾病预防控制中心官方微信公众号发布,应用SPSS 18.0软件进行数据分析.采用x2检验或Fisher确切概率法进行分类资料样本间率的比较,采用logistic多因素进行二元回归分析.结果 本次网络调查共收集有效应答问卷7011份,大众对新冠肺炎两个主要传播途径(呼吸道飞沫传播和接触传播)的认知率分别为99.7％和97.5％.不同年龄、职业在新冠肺炎基本特征、疾病严重程度的认知存在显著性差异.农民、务工人员和学生对传播途径和疾病主要特征的正确认知率均较低,18～29岁人群对"儿童症状较轻"的认知率最低(62.7％).73.3％的调查对象认为新冠肺炎"较重"或"很重",年轻、文化水平较高人群及医务人员中,认为新冠肺炎严重的比例低于年老或受教育程度低者.结论 大众普遍正确掌握新冠肺炎主要传播途径;不同年龄、职业的社会大众对新冠肺炎防控知识的认知存在显著性差异,这种差异会影响对新冠肺炎严重程度的判断.本次针对新冠肺炎的主动宣教效果显著,但除重视传统传播渠道外,应结合新媒体、标语等多种途径,对不同社交活跃程度的人群开展针对性宣传,以提高宣传效果,落实精准防控.

The studies on infectiousness of person infected with SARS-CoV-2 at different stages of illness are an important basis for making effective prevention and control measures such as investigating the infectious source, determining the scope of close contacts and the timing of case isolation. This review discusses the infectiousness of cases infected with SARS-CoV-2 in the incubation period, symptomatic period and convalescent period by reviewing national and international literatures, technical and professional guidelines. Existing researches suggest that the infectious viruses could be isolated at the end of the incubation period as well as since illness onset, and viral load in upper respiratory tract swabs reached the peak on day 4-6 after illness onset and thereafter began to decline, implying the infectiousness was relatively strong at the end of incubation period and within one week after illness onset. Although there were a few cases who tested positive for SARS-CoV-2 after recovery, no evidence was found to indicate these cases can cause the transmission.

An amendment to this paper has been published and can be accessed via the original article.

Domestic and foreign literatures related to the persistence of SARS-CoV-2 and the re-positive cases infected with SARS-CoV-2 were reviewed, and the characteristics and infectivity of the re-positive cases were analyzed to provide scientific evidence for the improvement of case management and the development of measures to stop the spread of SARS-CoV-2. Existing studies have shown that re-positive rate of SARS-CoV-2 ranged from 2.4% to 19.8%, the median of interval between re-positive detection and discharge was 4-15 days. Following the second course of the disease, the anti-SARS-CoV-2 IgM, IgG and IgA positive rates of the cases were 11.11%-86.08%, 52.00%-100.00% and 61.54%-100.00% respectively, the total antibody and neutralizing antibody positive rates were 98.72% and 88.46%. The viral load of the re-positive cases was lower than that in the initial infection. At least 3 380 re-positive cases have been reported globally. SARS-CoV-2 strains were isolated from the samples of 3 re-positive cases (1 immunodeficiency case and 2 cases with abnormal pulmonary imaging). There were close contacts that were infected by an asymptomatic case taking immunosuppressive agents. In conclusion, the infectivity of re-positive cases infected with SARS-CoV-2 is generally very low. Rare re-positive cases infected with SARS-CoV-2 might cause further transmission. The management approach for the re-positive cases can be based on the assessment of the individual transmission risk according to the pathogen detection results.

季节性流感（简称流感）是由季节性流感病毒引起的急性呼吸道传染病，流感病毒传播迅速，各年龄段人群均易感染，每年可引起季节性流行。流感的临床特征对于疾病的诊断和治疗具有重要意义，而儿童、成人和老年人群感染流感病毒后出现的临床特征存在差异，疾病严重程度也有所不同。本文通过对国内外不同年龄人群感染流感病毒后的临床特征和病情严重程度等研究进行归纳分析，以期对流感的及时识别、诊断和治疗提供证据支持。

Abstract Background The relative contributions of asymptomatic, pre-symptomatic and symptomatic transmission of SARS-CoV-2 have not been clearly measured although control measures may differ in response to the risk of spread posed by different types of cases. Methods We collected detailed information on transmission events and symptom status based on laboratory-confirmed patient data and contact tracing data from four provinces and one municipality in China. We estimated the variation in risk of transmission over time, and the severity of secondary infections, by symptomatic status of the infector. Results There were 393 symptomatic index cases with 3136 close contacts and 185 asymptomatic index cases with 1078 close contacts included into the study. The secondary attack rate among close contacts of symptomatic and asymptomatic index cases were 4.1% (128/3136) and 1.1% (12/1078), respectively, corresponding to a higher transmission risk from symptomatic cases than from asymptomatic cases (OR: 3.79, 95% CI: 2.06, 6.95). Approximately 25% (32/128) and 50% (6/12) of the infected close contacts were asymptomatic from symptomatic and asymptomatic index cases, respectively, while more than one third (38%) of the infections in the close contacts of symptomatic cases were attributable to exposure to the index cases before symptom onset. Infected contacts of asymptomatic index cases were more likely to be asymptomatic and less likely to be severe. Conclusions Asymptomatic and pre-symptomatic transmission play an important role in spreading infection, although asymptomatic cases pose a lower risk of transmission than symptomatic cases. Early case detection and effective test-and-trace measures are important to reduce transmission.

We estimated the symptomatic, PCR-confirmed secondary attack rate (SAR) for 2,382 close contacts of 476 symptomatic persons with coronavirus disease in Yichang, Hubei Province, China, identified during January 23–February 25, 2020. The SAR among all close contacts was 6.5%; among close contacts who lived with an index case-patient, the SAR was 10.8%; among close-contact spouses of index case-patients, the SAR was 15.9%. The SAR varied by close contact age, from 3.0% for those <18 years of age to 12.5% for those >60 years of age. Multilevel logistic regression showed that factors significantly associated with increased SAR were living together, being a spouse, and being >60 years of age. Multilevel regression did not support SAR differing significantly by whether the most recent contact occurred before or after the index case-patient’s onset of illness (p = 0.66). The relatively high SAR for coronavirus disease suggests relatively high virus transmissibility.