Transmission and containment of the SARS-CoV-2 Delta variant of concern in Guangzhou, China: A population-based study.

BACKGROUND: The first community transmission of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Delta variant of concern (VOC) in Guangzhou, China occurred between May and June 2021. Herein, we describe the epidemiological characteristics of this outbreak and evaluate the implemented containment measures against this outbreak. METHODOLOGY/PRINCIPAL FINDINGS: Guangzhou Center for Disease Control and Prevention provided the data on SARS-CoV-2 infections reported between 21 May and 24 June 2021. We estimated the incubation period distribution by fitting a gamma distribution to the data, while the serial interval distribution was estimated by fitting a normal distribution. The instantaneous effective reproductive number (Rt) was estimated to reflect the transmissibility of SARS-CoV-2. Clinical severity was compared for cases with different vaccination statuses using an ordinal regression model after controlling for age. Of the reported local cases, 7/153 (4.6%) were asymptomatic. The median incubation period was 6.02 (95% confidence interval [CI]: 5.42-6.71) days and the means of serial intervals decreased from 5.19 (95% CI: 4.29-6.11) to 3.78 (95% CI: 2.74-4.81) days. The incubation period increased with age (P<0.001). A hierarchical prevention and control strategy against COVID-19 was implemented in Guangzhou, with Rt decreasing from 6.83 (95% credible interval [CrI]: 3.98-10.44) for the 7-day time window ending on 27 May 2021 to below 1 for the time window ending on 8 June and thereafter. Individuals with partial or full vaccination schedules with BBIBP-CorV or CoronaVac accounted for 15.3% of the COVID-19 cases. Clinical symptoms were milder in partially or fully vaccinated cases than in unvaccinated cases (odds ratio [OR] = 0.26 [95% CI: 0.07-0.94]). CONCLUSIONS/SIGNIFICANCE: The hierarchical prevention and control strategy against COVID-19 in Guangzhou was timely and effective. Authorised inactivated vaccines are likely to contribute to reducing the probability of developing severe disease. Our findings have important implications for the containment of COVID-19.

Transmission risk of avian influenza virus along poultry supply chains in Guangdong, China.

OBJECTIVES: Avian influenza viruses (AIVs) poise significant risk to human health and the poultry industry. We evaluated the transmission risk along the poultry supply chain. METHODS: During October 2015 and July 2016, four rounds of cross-sectional surveys were performed to characterize AIV spread in farms, transport vehicles, slaughterhouses, wholesale and retail live poultry markets (LPMs). Poultry cloacal and oral swabs, environmental swabs, bioaerosol samples and human sera were collected. Poultry and environmental samples were tested for AIVs by rRT-PCR, further subtyped by next generation sequencing. Previous human H9N2 infections were identified by hemagglutination inhibition and microneutralization tests. Logistic regression was fitted to compare AIV transmission risk in different settings. RESULTS: AIVs was detected in 23.9% (424/1771) of the poultry and environmental samples. AIV detection rates in farms, transport vehicles, wholesale and retail LPMs were 4.5%, 11.1%, 30.3% and 51.2%, respectively. 5.2%, 8.3% and 12.8% of the poultry workers were seropositive in farms, wholesale and retail LPMs, respectively. The regression analysis showed that virus detection and transmission risk to human increased progressively along the poultry supply chain. CONCLUSIONS: Strengthening control measures at every level along the poultry supply chain, using a one health approach, is crucial to control AIV circulation.

Attitudinal changes toward control measures in live poultry markets among the general public and live poultry traders, Guangzhou, China, January-February, 2014.

Two sets of cross-sectional surveys were conducted among the general public and live poultry traders (LPTs) during January-February, 2014, to monitor attitudes toward human cases of avian influenza A(H7N9)-related control measures among these 2 parties in Guangzhou, China. We found generally high support for regular market rest days among the general public and LPTs, but only limited support for permanent central slaughtering of poultry. LPTs' support for relevant control measures declined after the citywide wet market closure.

[Investigation on the source of infection regarding an avian influenza (H5N1) case in Hong Kong that returning from Guangzhou].

OBJECTIVE: We conducted an epidemiologic investigation to determine the source of infection on an avian influenza (H5N1) case who returned from Guangzhou, in Hong Kong. METHODS: Data related to epidemiologic investigation, medical observation on close contacts, Syndromic Surveillance on poultry salesmen, emergency monitoring, detection of the samples, source tracing on potential Avian influenza virus (H5, H7, H9) infected people, situation on environment pollution by avian influenza virus in the markets etc. were gathered. The determination of infection source was through comparing the different genes between the case and positive environmental samples. RESULTS: The infected case witnessed the procedure of how a live duck was killed, in market A in Guangzhou during May 17(th) to 19(th). The case was diagnosed as respiratory tract infection in 2 Third-grade-Class A hospitals in Guangzhou on May 23(th) and 24(th). The diagnosis was made as Avian influenza cases on May 26(th) after going back to Hong Kong. 23 close contacts and 34 markets poultry salesmen did not show any ILI related symptoms. However, 2 poultry salesmen from the markets nearby the place where the Avian influenza case stayed, were detected having positive H9 avian influenza antibody, with the H9 positive rate as 6.06% (2/33). Among the environmental samples in the 2 markets nearby home of the patient, chopping block was found to have carried H5, with positive rate as 9.8% (5/51) while poultry cage was found to carry H9, with the positive rate as 2.0% (1/51). A H5 positive sample was found with clade 2.3.2.1, same to the case, from a chopping block at the market B where the sources of poultry was the same as market A. CONCLUSION: The source of infection seemed to come from the markets in Guangzhou, that calling for the strengthening of poultry market management, for avian influenza prevention. History related to contact of poultry should be gathered when a diagnosis of respiratory tract infection was made. Timely sampling and testing should be made to improve the sensitivity of diagnosis.

[Epidemiological characteristic of first case of locally identified A/H1N1 secondary cases caused by imported source of infection in China].

OBJECTIVE: To study the first locally identifed A/H1N1 secondary cases outbreak in China. METHODS: Interview and field investigation were integrated to describe the whole process of transmission on each case and to illustrate the relationships between the onset of the disease and the retated factors. RESULTS: Two contact persons appearanced fever and whose throat swabs were tested positive to H1N1 viral nucleic acid. The two had a history of contact in a short distance with the initial imported case without any protective measure in the poor air ventilation. The patients clinical situation was slight. The incubation was between 37 hours and 57 hours. No other new case was found after intervention as isolation and antisepsis were taken. CONCLUSION: This event was proved to be an outbreak of local A/H1N1 secondary cases caused by the imported case. The main mode of transmission was personal contact in a short distance without protection, through air and droplet. The locus with poor air ventilation was high risk place. Contact persons should be observed seven days and tested continuously. Infectivity and pathogenicity of the A/H1N1 virus were limited and appeared weakened by generations. Patient's condition was related with persistence and frequency of contact with the infection sources. Enhancing management of contact persons, health education, early diagnose, early treatment and early insulation were effective measures of controling and prenventing the spread A/H1N1.