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Background: Air pollution is a major risk factor for planetary health and has long been suspected of predisposing humans to respiratory diseases induced by pathogens like influenza viruses. However, epidemiological evidence remains elusive due to lack of longitudinal data from large cohorts., Objective: Our aim is to quantify the short-term association of influenza incidence with exposure to ambient air pollutants in Chinese cities., Methods: Based on air pollutant data and influenza surveillance data from 82 cities in China over a period of 5 years, we applied a two-stage time series analysis to assess the association of daily incidence of reported influenza cases with six common air pollutants [particulate matter with aerodynamic diameter ≤ 2.5 μ m ( PM 2.5 ), particulate matter with aerodynamic diameter ≤ 10 μ m ( PM 10 ), NO 2 , SO 2 , CO, and O 3 ], while adjusting for potential confounders including temperature, relative humidity, seasonality, and holiday effects. We built a distributed lag Poisson model for one or multiple pollutants in each individual city in the first stage and conducted a meta-analysis to pool city-specific estimates in the second stage., Results: A total of 3,735,934 influenza cases were reported in 82 cities from 2015 to 2019, accounting for 72.71% of the overall case number reported in the mainland of China. The time series models for each pollutant alone showed that the daily incidence of reported influenza cases was positively associated with almost all air pollutants except for ozone. The most prominent short-term associations were found for SO 2 and NO 2 with cumulative risk ratios of 1.094 [95% confidence interval (CI): 1.054, 1.136] and 1.093 (95% CI: 1.067, 1.119), respectively, for each 10   μ g / m 3 increase in the concentration at each of the lags of 1-7 d. Only NO 2 showed a significant association with the daily incidence of influenza cases in the multipollutant model that adjusts all six air pollutants together. The impact of air pollutants on influenza was generally found to be greater in children, in subtropical cities, and during cold months., Discussion: Increased exposure to ambient air pollutants, particularly NO 2 , is associated with a higher risk of influenza-associated illness. Policies on reducing air pollution levels may help alleviate the disease burden due to influenza infection. https://doi.org/10.1289/EHP12146.

Background: In the past few decades, globalization has rendered more frequent and intensive population movement between countries, which has changed the original disease spectrum and brought a huge health impact on the global population including China. This study aims to describe the spectrum and epidemiological characteristics of imported infections among foreign travelers travelling to China., Methods: The data on imported infections among foreign travelers were obtained from Custom Inbound Screening System (CISS) and the National Notifiable Infectious Disease Reporting System (NNIDRS). All the infections were classified into respiratory, gastrointestinal, vector-borne, blood/sex-transmitted and mucocutaneous diseases, of which case numbers and incidences were calculated and the proportions were compared among subgroups., Results: In total, 17,189 travelers diagnosed with 58 imported infectious diseases were reported from 2014 to 2018, with an overall incidence of 122.59 per million. Respiratory infection (7,351 cases, mainly influenza) and blood/sex-transmitted diseases (6,114 cases mainly Hepatitis B and HIV infection) were the most frequently diagnosed diseases, followed by vector-borne infections (3,128 cases, mainly dengue fever and malaria). The highest case number was from Asia and Europe, while the highest incidence rate was from Africa (296.00 per million). When specific diagnosis was compared, both the highest absolute case number and incidence were observed for influenza. An obvious seasonal pattern was observed for vector-borne diseases, with the annual epidemic spanning from July to November. The origin-destination matrices disclosed the movement of imported infection followed specific routes., Conclusions: Our study provided a profile of infectious diseases among foreign travelers travelling to China and pinpointed the target regions, seasons and populations for prevention and control, to attain an informed control of imported infections in China., (© 2022. The Author(s).)

We conducted a 3-year longitudinal serologic survey on an open cohort of poultry workers, swine workers, and general population controls to assess avian influenza A virus (AIV) seroprevalence and seroincidence and virologic diversity at live poultry markets (LPMs) in Wuxi City, Jiangsu Province, China. Of 964 poultry workers, 9 (0.93%) were seropositive for subtype H7N9 virus, 18 (1.87%) for H9N2, and 18 (1.87%) for H5N1. Of 468 poultry workers followed longitudinally, 2 (0.43%), 13 (2.78%), and 7 (1.5%) seroconverted, respectively; incidence was 1.27, 8.28, and 4.46/1,000 person-years for H7N9, H9N2, and H5N1 viruses, respectively. Longitudinal surveillance of AIVs at 9 LPMs revealed high co-circulation of H9, H7, and H5 subtypes. We detected AIVs in 726 (23.3%) of 3,121 samples and identified a high diversity (10 subtypes) of new genetic constellations and reassortant viruses. These data suggest that stronger surveillance for AIVs within LPMs and high-risk populations is imperative.

Avian influenza A(H7N9) virus has caused 5 epidemic waves in China since its emergence in 2013. We investigated the dynamic changes of antibody response to this virus over 1 year postinfection in 25 patients in Suzhou City, Jiangsu Province, China, who had laboratory-confirmed infections during the fifth epidemic wave, October 1, 2016-February 14, 2017. Most survivors had relatively robust antibody responses that decreased but remained detectable at 1 year. Antibody response was variable; several survivors had low or undetectable antibody titers. Hemagglutination inhibition titer was >1:40 for <40% of the survivors. Measured in vitro in infected mice, hemagglutination inhibition titer predicted serum protective ability. Our findings provide a helpful serologic guideline for identifying subclinical infections and for developing effective vaccines and therapeutics to counter H7N9 virus infections.

It has been documented that the epidemiological characteristics of human infections with H7N9 differ significantly between H5N1. However, potential factors that may explain the different spatial distributions remain unexplored. We use boosted regression tree (BRT) models to explore the association of agro-ecological, environmental and meteorological variables with the occurrence of human cases of H7N9 and H5N1, and map the probabilities of occurrence of human cases. Live poultry markets, density of human, coverage of built-up land, relative humidity and precipitation were significant predictors for both. In addition, density of poultry, coverage of shrub and temperature played important roles for human H7N9 infection, whereas human H5N1 infection was associated with coverage of forest and water body. Based on the risks and distribution of ecological characteristics which may facilitate the circulation of the two viruses, we found Yangtze River Delta and Pearl River Delta, along with a few spots on the southeast coastline, to be the high risk areas for H7N9 and H5N1. Additional, H5N1 risk spots were identified in eastern Sichuan and southern Yunnan Provinces. Surveillance of the two viruses needs to be enhanced in these high risk areas to reduce the risk of future epidemics of avian influenza in China.

Study Question: Can avian influenza A (H7N9) virus be transmitted between unrelated individuals in a hospital setting?, Methods: An epidemiological investigation looked at two patients who shared a hospital ward in February 2015, in Quzhou, Zhejiang Province, China. Samples from the patients, close contacts, and local environments were examined by real time reverse transcriptase (rRT) polymerase chain reaction (PCR) and viral culture. Haemagglutination inhibition and microneutralisation assays were used to detect specific antibodies to the viruses. Primary outcomes were clinical data, infection source tracing, phylogenetic tree analysis, and serological results., Study Answer and Limitations: A 49 year old man (index patient) became ill seven days after visiting a live poultry market. A 57 year old man (second patient), with a history of chronic obstructive pulmonary disease, developed influenza-like symptoms after sharing the same hospital ward as the index patient for five days. The second patient had not visited any poultry markets nor had any contact with poultry or birds within 15 days before the onset of illness. H7N9 virus was identified in the two patients, who both later died. Genome sequences of the virus isolated from both patients were nearly identical, and genetically similar to the virus isolated from the live poultry market. No specific antibodies were detected among 38 close contacts. Transmission between the patients remains unclear, owing to the lack of samples collected from their shared hospital ward. Although several environmental swabs were positive for H7N9 by rRT-PCR, no virus was cultured. Owing to delayed diagnosis and frequent hospital transfers, no serum samples were collected from the patients, and antibodies to H7N9 viruses could not be tested., What This Study Adds: Nosocomial H7N9 transmission might be possible between two unrelated individuals. Surveillance on patients with influenza-like illness in hospitals as well as chickens in live poultry markets should be enhanced to monitor transmissibility and pathogenicity of the virus., Funding, Competing Interests, Data Sharing: Funding support from the Program of International Science and Technology Cooperation of China (2013DFA30800), Basic Work on Special Program for Science and Technology Research (2013FY114600), National Natural Science Foundation of China (81402730), Special Program for Prevention and Control of Infectious Diseases in China (2013ZX10004218), US National Institutes of Health (1R01-AI108993), Zhejiang Province Major Science and Technology Program (2014C03039), and Quzhou Science and Technology Program (20111084). The authors declare no other interests and have no additional data., (© Fang et al 2015.)

Objectives: The rapid emergence, spread, and disease severity of avian influenza A (H7N9) in China has prompted concerns about a possible pandemic and regional spread in the coming months. The objective of this study was to predict the risk of future human infections with H7N9 in China and neighboring countries by assessing the association between H7N9 cases at sentinel hospitals and putative agricultural, climatic, and demographic risk factors., Methods: This cross-sectional study used the locations of H7N9 cases and negative cases from China's influenza-like illness surveillance network. After identifying H7N9 risk factors with logistic regression, we used Geographic Information Systems (GIS) to construct predictive maps of H7N9 risk across Asia., Results: Live bird market density was associated with human H7N9 infections reported in China from March-May 2013. Based on these cases, our model accurately predicted the virus' spread into Guangxi autonomous region in February 2014. Outside China, we find there is a high risk that the virus will spread to northern Vietnam, due to the import of poultry from China., Conclusions: Our risk map can focus efforts to improve surveillance in poultry and humans, which may facilitate early identification and treatment of human cases., (Copyright © 2014 The British Infection Association. All rights reserved.)

The outbreak of human infections with an emerging avian influenza A (H7N9) virus occurred in China in early 2013. It remains unknown what and how the underlying risk factors were involved in the bird-to-human cross-species transmission. To illustrate the dynamics of viral spread, we created a thematic map displaying the distribution of affected counties and plotted epidemic curves for the three most affected provinces and the whole country. We then collected data of agro-ecological, environmental and meteorological factors at the county level, and used boosted regression tree (BRT) models to examine the relative contribution of each factor and map the probability of occurrence of human H7N9 infection. We found that live poultry markets, human population density, irrigated croplands, built-up land, relative humidity and temperature significantly contributed to the occurrence of human infection with H7N9 virus. The discriminatory ability of the model was up to 97.4%. A map showing the areas with high risk for human H7N9 infection was created based on the model. These findings could be used to inform targeted surveillance and control efforts in both human and animal populations to reduce the risk of future human infections.

Data from all reported cases of 2009 pandemic influenza A (H1N1) were obtained from the China Information System for Disease Control and Prevention. The spatiotemporal distribution patterns of cases were characterized through spatial analysis. The impact of travel-related risk factors on invasion of the disease was analyzed using survival analysis, and climatic factors related to local transmission were identified using multilevel Poisson regression, both at the county level. The results showed that the epidemic spanned a large geographic area, with the most affected areas being in western China. Significant differences in incidence were found among age groups, with incidences peaking in school-age children. Overall, the epidemic spread from southeast to northwest. Proximity to airports and being intersected by national highways or freeways but not railways were variables associated with the presence of the disease in a county. Lower temperature and lower relative humidity were the climatic factors facilitating local transmission after correction for the effects of school summer vacation and public holidays, as well as population density and the density of medical facilities. These findings indicate that interventions focused on domestic travel, population density, and climatic factors could play a role in mitigating the public health impact of future influenza pandemics.

Objective: To study the epidemic tendency of emerging influenza A (H1N1) in mainland China, and to explore the different patterns of spread on the disease under the following contexts: (1) To stop the temperature screening program at the border areas of the country; (2) To stop measures of prevention and control on those identified cases and their close contacts; (3) To strengthen programs for the foreign immigrants on 'home quarantine'., Methods: Under relevant parameters and information on the transmission link from different reference data, the patterns of influenza spread were simulated by Monte Carlo method., Results: The temperature screening on border could inhibit the transmission of influenza A (H1N1) to some extent, so that after 3 months the cumulative number of cases will be reduced by 21.5% (1718 cases) and transmission speed of influenza A (H1N1) in mainland China will be delayed by about 4 days. Furthermore, taking positive measures of prevention and control could efficiently slow down the epidemic, so that after 3 months the cumulative number of cases will be reduced by 93.4% (about 90 thousand cases) and it would be delayed by about 15 days if influenza A (H1N1) spreads to the whole country. In addition, if the immigrants were able to practise quarantine measures consciously by themselves at home the effect of prevention and control against influenza A (H1N1) would be more significant. If 30%, 60% and 90% of immigrants would take quarantine measures home consciously, after 3 months the cumulative number of cases will be reduced by about 15% (about 940 cases), 34% (about 2230 cases) and 64% (about 4180 cases), respectively. Also, influenza A (H1N1) spreads to the whole country will be delayed by about 4 days, 10 days and 25 days, respectively. It is difficult to curb fully the development of the epidemic by taking existing control measures, and influenza A (H1N1) may spread to almost all provinces after about 3 months., Conclusion: The effects of existing prevention and control measures were objectively assessed and the results showed the necessity and effectiveness of these measures against the transmission of influenza A (H1N1), in the mainland of China.

Objective: To describe the epidemical characteristics of A (H1N1) influenza identified in the early stage (from May 11 to June 22, 2009) of the epidemic, in mainland China., Methods: Epidemical characteristics of 420 confirmed A (H1N1) influenza cases reported from May 11 to June 22, 2009 were analyzed descriptively, including the distribution of age, sex, source of infection, main symptoms and incubation period., Results: A total of 77.8% early cases in mainland China were imported from other countries. Three countries including America, Canada and Australia were attributed to 90% of the imported cases. Most of the cases were from 6 months to 73 years old, with 94% of them under 50 years. Most of the symptoms would include fever (81%), cough (40%) and sore throat (35%). The mean incubation period of second-generation cases was 4.3 (4.2 +/- 1.5) days., Conclusion: Imported cases dominated the total cases in the early stage of the epidemic had similar gender distribution of those from exporting countries. Fever, cough and sore throat were the three main symptoms manifested in influenza cases. 2.5 +/- 1.9 (1 - 11) days was found in imported cases between the day of off-board and the onset of symptoms. The incubation period was 4.3 +/- 1.7 (1 - 8) days among the secondary cases.

Objective: To study the spatiotemporal distribution and seasonal characteristics of influenza and to explore its transmission patterns, in the mainland of China., Methods: Spatiotemporal cluster methods and spatial trend surface methods were used to analyze the influenza surveillance data., Results: There were a summer peak in the south from June to August (RR(paediatric) = 1.31, P < 0.01; RR(internal) = 1.74, P < 0.01) and a winter peak from December to January (RR(paediatric) = 1.45, P < 0.01; RR(internal) = 1.45, P < 0.01) in the northern part of the country, during every epidemic season. Influenza virus in mainland China seemed to spread from the southern to the northern parts of the country, in a progressing way., Conclusion: In the southern part of the country, it is more important to take prevention and control measurements on influenza from June to August but for the northern part, the key period is from December to January. It is more important to timely identify the variation of the influenza virus, in the southern part of the country.