Epidemiological analysis of respiratory viral etiology for influenza-like illness during 2010 in Zhuhai, China

Abstract

Background: Influenza-like illnesses (ILI), a subset of acute respiratory infections (ARI), are a significant source of morbidity and mortality worldwide. ILI can be caused by numerous pathogens, however; there is limited information on the etiology and epidemiology of ILI in China.

Methods: We performed a one-year surveillance study (2010) of viral etiology causing ILI and investigated the influence of climate on outbreaks of ILI attributed to viruses at the Outpatient Department of Zhuhai Municipal People's Hospital in Zhuhai, China.

Results: Of the 337,272 outpatients who sought attention in the Outpatient Department of Zhuhai Municipal People's Hospital in 2010, 3,747 (1.11%) presented with ILI. Of these patients presenting with ILI, 24.66% (924/3,747) had available samples and were enrolled in this study. At least one respiratory virus was identified in 411 patients (44.48%) and 42 (4.55%) were co-infected with two viruses. In patients co-infected with two viruses, respiratory syncytial virus (RSV) was detected in 50% (21/42). Among common viral pathogens detected, significant differences in age distributions were observed in seasonal influenza virus A (sFulA, H3N2) and B (sFluB), pandemic H1N1 2009 influenza viruses (H1N1pdm09), RSV, and adenovirus (ADV). Infections with sFluA (H3N2), sFluB, RSV, and human metapneumovirus (HMPV) had characteristic seasonal patterns. The incidences of sFluA (H3N2), ADV, and RSV correlated with air temperature. Alternatively, the incidence of sFluB correlated with relative air humidity.

Conclusions: These results demonstrate that a wide range of respiratory viral pathogens are circulating in Zhuhai city. This information needs to be considered by clinicians when treating patients presenting with ILI.

Figure 1

The monthly distribution of ILI in outpatients by age group during 2010. Of 337,272 outpatients who sought attention in the Outpatient Department of Zhuhai Municipal People’s Hospital, 3,747 (1.11%) presented with ILI in 2010. The prevalence of ILI (%) is shown for each month of 2010, divided into five different age categories.

Figure 2

Gender distribution of respiratory viral infection in 924 patients with ILI. Of 924 patients with ILI, 540 (58.44%) were male and 384 (41.56%) female. Respiratory tract viruses were detected in 231 (46.80%) of the male patients and 181 (47.14%) of the female (P = 0.189, not significant). The age distribution is shown for each viral pathogen tested. Male = purple, female = blue.

Figure 3

Monthly distribution of respiratory viral infection in 924 patients with ILI. Each viral pathogen tested in our study was plotted for each month in 2010. The percent of admitted patients infected is shown on the y axis as a function of the month on the x axis. In China, the four seasons were generally recognized as spring (March–May), summer (June–August), fall (September–November), and winter (December–February). Respiratory viral agents usually have characteristic seasonal patterns. The peak of sFluA (H3N2) was from August–September, sFluB from March–May, and the peak of H1N1pdm09 occurred in January. RSV infection occurred predominantly from December–February and usually was observed in co-infection with sFluA, sFluB, HMPV, and ADV. PIV and ADV were detected throughout the year without significant seasonality in 2010.

Figure 4

The distribution of respiratory viral pathogens in the local climate of Zhuhai during 2010. Zhuhai is located in the southern tip of Mainland China and is a subtropical coastal city with a humid climate and small diurnal air temperature range. The average monthly air temperature ranged 16–29.4°C and the average monthly relative humidity varied between 65.9-90.8% in Zhuhai during 2010. When the temperature rose, the number of patients infected with sFluA (H3N2) and ADV increased significantly (r = 0.592, P = 0.043 and r = 0.699, P = 0.011; respectively). Alternatively, the colder the temperature became, the number of patients infected with RSV increased (r = 0.699, P = 0.011). In addition, the prevalence of sFluB was significantly, positively correlated with air relative humidity (r = 0.697, P < 0.001).