Comparative epidemiology of outbreaks caused by SARS-CoV-2 Delta and Omicron variants in China.

From 2020 to December 2022, China implemented strict measures to contain the spread of severe acute respiratory syndrome coronavirus 2. However, despite these efforts, sustained outbreaks of the Omicron variants occurred in 2022. We extracted COVID-19 case numbers from May 2021 to October 2022 to identify outbreaks of the Delta and Omicron variants in all provinces of mainland China. We found that omicron outbreaks were more frequent (4.3 vs. 1.6 outbreaks per month) and longer-lasting (mean duration: 13 vs. 4 weeks per outbreak) than Delta outbreaks, resulting in a total of 865,100 cases, of which 85% were asymptomatic. Despite the average Government Response Index being 12% higher (95% confidence interval (CI): 9%, 15%) in Omicron outbreaks, the average daily effective reproduction number (Rt) was 0.45 higher (95% CI: 0.38, 0.52, p < 0.001) than in Delta outbreaks. Omicron outbreaks were suppressed in 32 days on average (95% CI: 26, 39), which was substantially longer than Delta outbreaks (14 days; 95% CI: 11, 19; p = 0.004). We concluded that control measures effective against Delta could not contain Omicron outbreaks in China. This highlights the need for continuous evaluation of new variants' epidemiology to inform COVID-19 response decisions.

Latent and incubation periods of Delta, BA.1, and BA.2 variant cases and associated factors: a cross-sectional study in China.

BACKGROUND: The latent and incubation periods characterize the transmission of infectious viruses and are the basis for the development of outbreak prevention and control strategies. However, systematic studies on the latent period and associated factors with the incubation period for SAS-CoV-2 variants are still lacking. We inferred the two durations of Delta, BA.1, and BA.2 cases and analyzed the associated factors. METHODS: The Delta, BA.1, and BA.2 (and its lineages BA.2.2 and BA.2.76) cases with clear transmission chains and infectors from 10 local SAS-CoV-2 epidemics in China were enrolled. The latent and incubation periods were fitted by the Gamma distribution, and associated factors were analyzed using the accelerated failure time model. RESULTS: The mean latent period for 672 Delta, 208 BA.1, and 677 BA.2 cases was 4.40 (95%CI: 4.24 ~ 4.63), 2.50 (95%CI: 2.27 ~ 2.76), and 2.58 (95%CI: 2.48 ~ 2.69) days, respectively, with 85.65% (95%CI: 83.40 ~ 87.77%), 97.80% (95%CI: 96.35 ~ 98.89%), and 98.87% (95%CI: 98.40 ~ 99.27%) of them starting to shed viruses within 7 days after exposure. In 405 Delta, 75 BA.1, and 345 BA.2 symptomatic cases, the mean latent period was 0.76, 1.07, and 0.79 days shorter than the mean incubation period [5.04 (95%CI: 4.83 ~ 5.33), 3.42 (95%CI: 3.00 ~ 3.89), and 3.39 (95%CI: 3.24 ~ 3.55) days], respectively. No significant difference was observed in the two durations between BA.1 and BA.2 cases. After controlling for the sex, clinical severity, vaccination history, number of infectors, the length of exposure window and shedding window, the latent period [Delta: exp(ß) = 0.81, 95%CI: 0.66 ~ 0.98, p = 0.034; Omicron: exp(ß) = 0.82, 95%CI: 0.71 ~ 0.94, p = 0.004] and incubation period [Delta: exp(ß) = 0.69, 95%CI: 0.55 ~ 0.86, p < 0.001; Omicron: exp(ß) = 0.83, 95%CI: 0.72 ~ 0.96, p = 0.013] were significantly shorter in 18 ~ 49 years but did not change significantly in ≥ 50 years compared with 0 ~ 17 years. CONCLUSION: Pre-symptomatic transmission can occur in Delta, BA.1, and BA.2 cases. The latent and incubation periods between BA.1 and BA.2 were similar but shorter compared with Delta. Age may be associated with the latent and incubation periods of SARS-CoV-2.

Effectiveness of social distancing measures and lockdowns for reducing transmission of COVID-19 in non-healthcare, community-based settings.

Social distancing measures (SDMs) are community-level interventions that aim to reduce person-to-person contacts in the community. SDMs were a major part of the responses first to contain, then to mitigate, the spread of SARS-CoV-2 in the community. Common SDMs included limiting the size of gatherings, closing schools and/or workplaces, implementing work-from-home arrangements, or more stringent restrictions such as lockdowns. This systematic review summarized the evidence for the effectiveness of nine SDMs. Almost all of the studies included were observational in nature, which meant that there were intrinsic risks of bias that could have been avoided were conditions randomly assigned to study participants. There were no instances where only one form of SDM had been in place in a particular setting during the study period, making it challenging to estimate the separate effect of each intervention. The more stringent SDMs such as stay-at-home orders, restrictions on mass gatherings and closures were estimated to be most effective at reducing SARS-CoV-2 transmission. Most studies included in this review suggested that combinations of SDMs successfully slowed or even stopped SARS-CoV-2 transmission in the community. However, individual effects and optimal combinations of interventions, as well as the optimal timing for particular measures, require further investigation. This article is part of the theme issue 'The effectiveness of non-pharmaceutical interventions on the COVID-19 pandemic: the evidence'.

Famine exposure in early life and type 2 diabetes in adulthood: findings from prospective studies in China.

BACKGROUND/OBJECTIVES: This study examined the relationship between famine exposure in early life and the risk of type 2 diabetes in adulthood during the 1959-1961 Chinese Famine. SUBJECTS/METHODS: A total of 3,418 individuals aged 35-74 years free of diabetes from two studies in 2006 and 2009 were followed up prospectively in 2009 and 2012, respectively. Famine exposure was classified as unexposed (individuals born in 1962-1978), fetal exposed (individuals born in 1959-1961), child exposed (individuals born in 1949-1958), and adolescent/adult exposed (born in 1931-1948). A logistic regression model was used to assess the relationship between famine exposure and diabetes after adjustment for potential covariates. RESULTS: During a three-year follow-up, the age-adjusted incidence rates of type 2 diabetes were 5.7%, 14.5%, 12.7%, and 17.8% in unexposed, fetal-exposed, child-exposed, and adolescent/adult-exposed groups, respectively (P < 0.01). Relative to the unexposed group, the relative risks (95% confidence interval) for diabetes were 2.15 (1.29-3.60), 1.53 (0.93-2.51), and 1.65 (0.75-3.63) in the fetal-exposed, child-exposed, and adolescent/adult-exposed groups, after controlling for potential covariates. The interactions between famine exposure and obesity, education level, and family history of diabetes were not observed, except for the urbanization type. Individuals living in rural areas with fetal and childhood famine exposure were at a higher risk of type 2 diabetes, with relative risks of 8.79 (1.82-42.54) and 2.33 (1.17-4.65), respectively. CONCLUSIONS: These findings indicate that famine exposure in early life is an independent predictor of type 2 diabetes, particularly in women. Early identification and intervention may help prevent diabetes in later life. Trial Registration: ClinicalTrials.gov Identifier: NCT01053195.

The Omicron Variant Reinfection Risk among Individuals with a Previous SARS-CoV-2 Infection within One Year in Shanghai, China: A Cross-Sectional Study.

Reinfection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants due to immune escape is challenging for the global response to the pandemic. We estimated the Omicron reinfection prevalence among people who had a previous SARS-CoV-2 infection in Shanghai, China. We conducted a telephone survey in December 2022 with those who had previously been infected with Omicron between March and May 2022. Information on their demographics, coronavirus disease 2019 (COVID-19) testing, and vaccination history was collected. The overall and subgroup reinfection rates were estimated and compared. Among the 1981 respondents who were infected between March and May 2022, 260 had positive nucleic acid or rapid antigen tests in December 2022, with an estimated reinfection rate of 13.1% (95% confidence interval [95% CI]: 11.6-14.6). The reinfection rate for those who had a booster vaccination was 11.4% (95% CI: 9.2-13.7), which was significantly lower than that for those with an incomplete vaccination series (15.2%, 95% CI: 12.3-18.1) (adjusted odds ratio [aOR]: 0.579; 95% CI: 0.412-0.813). Reinfection with the Omicron variant was lower among individuals with a previous SARS-CoV-2 infection and those who had a booster vaccination, suggesting that hybrid immunity may offer protection against reinfection with Omicron sublineages.

Hospitalizations and mortality during the first year of the COVID-19 pandemic in Hong Kong, China: An observational study.

Background: Hong Kong followed a strict COVID-19 elimination strategy in 2020. We estimated the impact of the COVID-19 pandemic responses on all-cause and cause-specific hospitalizations and deaths in 2020. Methods: Interrupted time-series analysis using negative binomial regression accounting for seasonality and long-term trend was used on weekly 2010-2020 data to estimate the change in hospitalization risk and excess mortality occurring both within and out of hospitals. Findings: In 2020, as compared to a 2010-2019 baseline, we observed an overall reduction in all-cause hospitalizations, and a concurrent increase in deaths. The overall hospitalization reduction (per 100,000 population) was 4809 (95% CI: 4692, 4926) in 2020, with respiratory diseases (632, 95% CI: 607, 658) and cardiovascular diseases (275, 95% CI: 264, 286) contributing most. The overall excess mortality (per 100,000 population) was 25 (95% CI: 23, 27) in 2020, mostly among individuals with pre-existing cardiovascular diseases (12, 95% CI: 11, 13). A reduction in excess in-hospital mortality (-10 per 100,000, 95% CI: -12, -8) was accompanied by an increase in excess out-of-hospital mortality (32, 95% CI: 29, 34). Interpretation: The COVID-19 pandemic might have caused indirect impact on population morbidity and mortality likely through changed healthcare seeking particularly in youngest and oldest individuals and those with cardiovascular diseases. Better healthcare planning is needed during public health emergencies with disruptions in healthcare services. Funding: Health and Medical Research Fund, Collaborative Research Fund, AIR@InnoHK and RGC Senior Research Fellow Scheme, Hong Kong.

Transmission dynamics of SARS-CoV-2 Omicron variant infections in Hangzhou, Zhejiang, China, January-February 2022.

OBJECTIVES: We aimed to explore the transmission dynamics of the Omicron BA.1.1 variant in an outbreak in China. METHODS: We constructed 113 transmission pairs based on the time of exposure and symptom onset for identified infectors and infectees, using the epidemiological data collected during an outbreak in Hangzhou, Zhejiang province, China, between January and February 2022. The key epidemiological parameters were estimated. RESULTS: The mean estimates of the incubation period and latent period distributions were 3.8 days (95% credible interval: 3.5, 4.1) and 3.1 days (2.8, 3.5), respectively. The overall transmission risk peaked at symptom onset, and we estimated that 33.6% (24.8, 42.5) of transmission occurred before symptom onset. The forward generation time decreased from 5.2 days (4.7, 5.7) at the start of the outbreak to 2.2 days (2.0, 2.5) by the end. Allowing this variation over time in the generation time distribution, we estimated that the reproduction number dropped rapidly from 9.5 (3.5, 18.4) to 0.8 (0.3, 1.5) over the outbreak. CONCLUSION: Shorter incubation period and latent period were estimated for the Omicron BA.1.1 variant. Stringent public health measures prevented a large epidemic by reducing transmission, as indicated by the shortened generation time.

Transmission dynamics and epidemiological characteristics of SARS-CoV-2 Delta variant infections in Guangdong, China, May to June 2021.

BackgroundThe Delta variant of SARS-CoV-2 had become predominant globally by November 2021.AimWe evaluated transmission dynamics and epidemiological characteristics of the Delta variant in an outbreak in southern China.MethodsData on confirmed COVID-19 cases and their close contacts were retrospectively collected from the outbreak that occurred in Guangdong, China in May and June 2021. Key epidemiological parameters, temporal trend of viral loads and secondary attack rates were estimated. We also evaluated the association of vaccination with viral load and transmission.ResultsWe identified 167 patients infected with the Delta variant in the Guangdong outbreak. Mean estimates of latent and incubation period were 3.9 days and 5.8 days, respectively. Relatively higher viral load was observed in infections with Delta than in infections with wild-type SARS-CoV-2. Secondary attack rate among close contacts of cases with Delta was 1.4%, and 73.1% (95% credible interval (CrI): 32.9-91.4) of the transmissions occurred before onset. Index cases without vaccination (adjusted odds ratio (aOR): 2.84; 95% CI: 1.19-8.45) or with an incomplete vaccination series (aOR: 6.02; 95% CI: 2.45-18.16) were more likely to transmit infection to their contacts than those who had received the complete primary vaccination series.DiscussionPatients infected with the Delta variant had more rapid symptom onset compared with the wild type. The time-varying serial interval should be accounted for in estimation of reproduction numbers. The higher viral load and higher risk of pre-symptomatic transmission indicated the challenges in control of infections with the Delta variant.

Clonorchis sinensis Reinfection Rate and Reinfection Determinants: A Prospective Cohort Study in Hengxian County, Guangxi, China.

BACKGROUND: To understand Clonorchis sinensis reinfection and the determinants of reinfection in endemic areas is important in establishment of control measures. METHODS: A prospective cohort study was implemented in Hengxian County, Guangxi, China. Individuals with C. sinensis infection were completely treated, and those cured were enrolled as study subjects and followed up for 3, 6, and 12 months. The reinfection frequency and incidence were calculated, and a multivariable Cox proportional hazard model was constructed to capture reinfection determinants. RESULTS: Among 635 enrolled subjects, 436 (68.7%) completed follow-up. Of these, 177 (40.6%) were reinfected; 133 (75.1%) were reinfected once, 41 (23.2%) twice, and 3 (1.7%) three times. The incidence of reinfection was 64.0 per 100 person-years. Men (adjusted hazard ratio [aHR], 1.67; 95% confidence interval [CI], 1.14-2.44), those with underlying diseases (aHR, 1.41; 95% CI, 1.02-1.95), and those with moderate- or heavy-intensity infections (aHR, 1.45; 95% CI, 1.14-1.85) had increasing reinfection probabilities. CONCLUSIONS: C. sinensis reinfection is high in endemic areas. Men and high-intensity infection are important determinants of reinfection. Repeated chemotherapy is necessary to control reinfection and its associated morbidities, especially in high-risk individuals. In addition, behavioral education is advised to decrease overall reinfection in endemic areas.

Estimating the Latent Period of Coronavirus Disease 2019 (COVID-19).

Using detailed exposure information on COVID-19 cases, we estimated the mean latent period to be 5.5 (95% CI: 5.1-5.9) days, shorter than the mean incubation period (6.9 days). Laboratory testing may allow shorter quarantines since 95% of COVID-19 cases shed virus within 10.6 (95% CI: 9.6-11.6) days of infection.

The Incubation Period Distribution of Coronavirus Disease 2019: A Systematic Review and Meta-analysis.

Incubation period is an important parameter to inform quarantine period and to study transmission dynamics of infectious diseases. We conducted a systematic review and meta-analysis on published estimates of the incubation period distribution of coronavirus disease 2019, and showed that the pooled median of the point estimates of the mean, median and 95th percentile for incubation period are 6.3 days (range, 1.8-11.9 days), 5.4 days (range, 2.0-17.9 days), and 13.1 days (range, 3.2-17.8 days), respectively. Estimates of the mean and 95th percentile of the incubation period distribution were considerably shorter before the epidemic peak in China compared to after the peak, and variation was also noticed for different choices of methodological approach in estimation. Our findings implied that corrections may be needed before directly applying estimates of incubation period into control of or further studies on emerging infectious diseases.

Epidemiological Characteristics of Hand, Foot, and Mouth Disease Outbreaks in Qingdao, 2009-2018.

BACKGROUND: In China, hand, foot, and mouth disease (HFMD) outbreaks have become an important issue recent years. We analyzed the epidemiological characteristics of HFMD outbreaks in Qingdao during 2009-2018, and provided evidences for prevention and control of the disease. METHODS: Data were analyzed by descriptive analysis and correlation analysis, and throat swabs were detected for enterovirus RNA using RT-PCR. RESULTS: Overall, 116 HFMD outbreaks were reported in Qingdao during 2009-2018, with the epidemic of the outbreaks exhibiting a decreasing tendency. The characteristics of outbreaks presented two patterns, including two-peak pattern and rural area to urban-rural fringe area to urban areas pattern. Male patients were predominant in these outbreaks. The location of the outbreaks changed from nursery to community. Non-EV71/CA16 enteroviruses were gradually becoming predominant enteroviruses serotypes. The durations of outbreaks were positively correlated with response times and the number of cases. CONCLUSION: The epidemiological characteristics analysis of HFMD outbreaks could provide a scientific basis for the prevention and control the disease. Reporting and handling promptly are the keys to control epidemic outbreaks of HFMD.

An investigation of Human Clonorchiasis prevalence in an Endemic County in Guangxi Zhuang Autonomous Region, China, 2016.

To effectively promote the implementation of interventions, the identification of high-risk groups and the characteristics of Clonorchis sinensis infection in endemic regions are needed. In a clonorchiasis-endemic area, local residents were randomly enrolled for helminth egg examination in June 2016. The prevalence in subpopulations as well as the knowledge, attitudes, and behaviours and the factors influencing clonorchiasis in egg-positive populations were analysed. A total of 2282 local residents participated in the survey; the C. sinensis prevalence was 48.6% (1109 persons). A higher prevalence was found in males (62.6%) than in females (29.7%). People older than 30 years had the highest prevalence (52.7%-57.6%). Among the 888 persons who were infected with C. sinensis and participated the questionnaire investigation, 19.0% (169/888) knew that it could cause cancer. In addition, 60.6% of people reported that they intended to keep eating raw fish despite knowing the risk of infection. The two primary reasons for continuing to eat raw fish were the disease being regarded as not serious (38.3%) and the belief that anti-parasite medications are effective (39.6%). A total of 94.4% (797/844) of responders reported eating raw fish more frequently in the home than outside of the home. Our study revealed a notably high C. sinensis prevalence in the study area. Awareness of clonorchiasis disease severity should be increased among high-risk individuals and families in highly endemic areas.

Risk factors associated with occurrence of COVID-19 among household persons exposed to patients with confirmed COVID-19 in Qingdao Municipal, China.

Tracing and isolation of close contacts is used to control outbreaks of coronavirus disease 2019 (COVID-19) in China. However, risk factors associated with the occurrence of COVID-19 among close contacts have not been well described. A total of 106 household contacts were included in this study, of whom 19 developed into COVID-19 cases, and the secondary attack rate was 17.9%. Multivariable analysis showed that increasing risk of occurrence of COVID-19 among household contacts was associated with female index patients (adjusted hazard ratio [aHR] = 3.84, 95% CI = 1.07-13.78), critical disease index patients (aHR = 7.58, 95% CI = 1.66-34.66), effective contact duration with index patients > 2 days (aHR = 4.21, 95% CI = 1.29-13.73), and effective contact duration > 11 days (aHR = 17.88, 95% CI = 3.26-98.01). The sex and disease severity of index patients with COVID-19 and longer effective contact duration with patients with confirmed COVID-19 could help epidemiologists to identify potential COVID-19 cases among household contacts at an early stage.

Associations between anthropometric parameters (body mass index, waist circumference and waist to hip ratio) and newly diagnosed hyperuricemia in adults in Qingdao, China: A cross-sectional study.

BACKGROUND AND OBJECTIVES: To evaluate the association between anthropometric parameter of obesity and newly diagnosed hyperuricemia (HUA) in a general Chinese population. METHODS AND STUDY DESIGN: A population- based cross-sectional survey included 9 615 participants (3777 men and 5838 women) aged 35-74 years in 2006 and 2009 in Qingdao, China. The multivariate linear regression was used to assess the linear associations between anthropometric parameter of obesity [body mass index (BMI), waist circumference (WC), waist-to-hip ratio (WHR)] and serum uric acid. The logistic regression model was performed to estimate the associations between BMI, WC, WHR and newly diagnosed HUA. RESULTS: The prevalence of newly diagnosed HUA was higher in men than in women (19.46% vs 11.34%, p<0.05). Multivariate liner regression showed that BMI, WC and WHR were positively correlated with serum uric acid. Multivariate logistic regression revealed that being overweight [men, odds ratios (OR): 1.69, 95% confidence intervals (95% CI): 1.37-2.08; women, OR: 1.67, 95% CI: 1.34-2.09] and obese (men, OR: 3.01, 95% CI: 2.38-3.79; women, OR: 2.91, 95% CI: 2.31-3.67) were significantly associated with a higher risk of newly diagnosed HUA. Abdominal obesity (WC: men, OR: 2.26, 95% CI: 1.88-2.73; women, OR: 1.96, 95% CI: 1.61-2.39; WHR: men, OR: 1.91, 95% CI: 1.61-2.26; women, OR: 1.39, 95% CI: 1.16-1.67) were associated with an increased risk of newly diagnosed HUA. CONCLUSIONS: This study demonstrated that BMI, WC and WHR were positively correlated with serum uric acid in both genders. Meanwhile, overweight, obese and abdominal obesity were associated with increased risk of newly diagnosed HUA.

Risk mapping of scrub typhus infections in Qingdao city, China.

BACKGROUND: The emergence and re-emergence of scrub typhus has been reported in the past decade in many global regions. In this study, we aim to identify potential scrub typhus infection risk zones with high spatial resolution in Qingdao city, in which scrub typhus is endemic, to guide local prevention and control strategies. METHODOLOGY/PRINCIPAL FINDINGS: Scrub typhus cases in Qingdao city during 2006-2018 were retrieved from the Chinese National Infectious Diseases Reporting System. We divided Qingdao city into 1,101 gridded squares and classified them into two categories: areas with and without recorded scrub typhus cases. A boosted regression tree model was used to explore environmental and socioeconomic covariates associated with scrub typhus occurrence and predict the risk of scrub typhus infection across the whole area of Qingdao city. A total of 989 scrub typhus cases were reported in Qingdao from 2006-2018, with most cases located in rural and suburban areas. The predicted risk map generated by the boosted regression tree models indicated that the highest infection risk areas were mainly concentrated in the mid-east and northeast regions of Qingdao, with gross domestic product (20.9%±1.8% standard error) and annual cumulative precipitation (20.3%±1.1%) contributing the most to the variation in the models. By using a threshold environmental suitability value of 0.26, we identified 757 squares (68.7% of the total) with a favourable environment for scrub typhus infection; 66.2% (501/757) of the squares had not yet recorded cases. It is estimated that 6.32 million people (72.5% of the total population) reside in areas with a high risk of scrub typhus infection. CONCLUSIONS/SIGNIFICANCE: Many locations in Qingdao city with no recorded scrub typhus cases were identified as being at risk for scrub typhus occurrence. In these at-risk areas, awareness and capacity for case diagnosis and treatment should be enhanced in the local medical service institutes.

High endemicity of Clonorchis sinensis infection in Binyang County, southern China.

High-intensity clonorchiasis infection is associated with serious outcomes, including cancer. Understanding the infection intensity of Clonorchis sinensis and its risk factors in local endemic regions could facilitate effective control measures. In a county located in a highly endemic area in Guangxi Province, P. R. China, local residents were randomly enrolled in the study; helminth egg examinations were performed with the Kato-Katz method, and the intensity of infection was identified as mild, moderate or heavy. Knowledge, attitudes, and high-risk behaviours were investigated among those infected with Clonorchis sinensis. A total of 2521 local residents participated in this study, and the Clonorchis sinensis-positive proportion was 28.9% (728 persons). Among the infected persons, the percentages of mild, moderate and heavy infections were 66.2%, 28.4% and 5.4%, respectively. Males experienced a higher proportion of moderate and heavy infections (37.5%) than females (18.1%) (p<0.05). The highest infection proportion among the different levels of infection intensity was identified among persons aged 30-59 years (15.7% for moderate and heavy infections). Among the 509 persons who reported eating raw fish, 302 persons (59.3%) had eaten raw fresh fish for more than 10 years, and 131 (25.7%) persons ate raw fish ≥12 times a year. Multivariate logistic regression revealed that eating raw fish 12-50 times in the last year (adjusted odds ratio [aOR] = 1.74, 95%CI: 1.09-2.80) and eating raw fish >50 times in the last year (aOR = 2.89, 95%CI: 1.20-7.50) were risk factors for high-intensity infections (moderate and heavy). The overall infection proportion was high in the study area, with a large group of residents experiencing high-intensity infections. High frequency of raw fish consumption was associated with high-intensity infections. Intervention strategies targeting people with a high frequency of raw fish consumption should be implemented to reduce the probability of severe consequences.

Epidemiologic Changes of Scrub Typhus in China, 1952-2016.

Scrub typhus, a miteborne rickettsiosis, has emerged in many areas globally. We analyzed the incidence and spatial-temporal distribution of scrub typhus in China during 1952-1989 and 2006-2016 using national disease surveillance data. A total of 133,623 cases and 174 deaths were recorded. The average annual incidence was 0.13 cases/100,000 population during 1952-1989; incidence increased sharply from 0.09/100,000 population in 2006 to 1.60/100,000 population in 2016. The disease, historically endemic to southern China, has expanded to all the provinces across both rural and urban areas. We identified 3 distinct seasonal patterns nationwide; infections peaked in summer in the southwest, summer-autumn in the southeast, and autumn in the middle-east. Persons >40 years of age and in nonfarming occupations had a higher risk for death. The changing epidemiology of scrub typhus in China warrants an enhanced disease control and prevention program.

Spatiotemporal and demographic characteristics of scrub typhus in Southwest China, 2006-2017: An analysis of population-based surveillance data.

Scrub typhus is a life-threatening vector-borne disease. During the past decade, the number of areas affected by this disease has expanded in many countries. In this study, we aim to identify the spatiotemporal and demographic characteristics of scrub typhus in Southwest China, an emerging endemic region for scrub typhus. Population-based surveillance data capturing scrub typhus cases in two provinces of Southwest China during 2006-2017 were retrieved. Descriptive temporal and spatial analyses were conducted and stratified by age group. The space-time scan statistic was used to identify spatiotemporal clusters of scrub typhus occurrence at the county level. During the study period, 30,001 scrub typhus cases were recorded in Southwest China, with a total of 61.0% (191/313) of counties being affected; most cases (94.3%) occurred in rural areas. The annual incidence rate increased substantially from 0.25/100,000 in 2006 to 5.38/100,000 in 2017 (>21-fold change). The 0- to 4-year-old and 45- to 64-year-old subgroups had the highest cumulative incidence rates (57.46 and 32.98/100,000, respectively). Furthermore, since 2006, the 0- to 4-year-old (slope = 0.83, p < .01) and 45-64-year-old (slope = 0.69, p < .01) age groups have had the highest increases in incidence of all age groups. The most likely spatial cluster of overall cases (relative risk = 4.13, p < .01) occurred in the southern region of Southwest China and included 41 high-risk counties. In conclusion, scrub typhus appears to be widely distributed and rapidly increasing in Southwest China. Young children and middle-aged adults were the most severely affected groups, and the disease appeared to predominantly cluster in the southern part of Southwest China. Further in-depth surveys to determine the epidemiological characteristics and driving factors of this emerging disease and to facilitate effective control programmes among high-risk groups in the affected areas should be promoted.