Respiratory Syncytial Virus Seasonality, Beijing, China, 2007-2015

Abstract

During July 2007-June 2015, we enrolled 4,225 hospitalized children with pneumonia in a study to determine the seasonality of respiratory syncytial virus (RSV) infection in Beijing, China. We defined season as the period during which >10% of total PCRs performed each week were RSV positive. We identified 8 distinctive RSV seasons. On average, the season onset occurred at week 41 (mid-October) and lasted 33 weeks, through week 20 of the next year (mid-May); 97% of all RSV-positive cases occurred during the season. RSV seasons occurred 3-5 weeks earlier and lasted ≈6 weeks longer in RSV subgroup A-dominant years than in RSV subgroup B-dominant years. Our analysis indicates that monitoring such RSV subgroup shifts might provide better estimates for the onset of RSV transmission. PCR-based tests could be a flexible or complementary way of determining RSV seasonality in locations where RSV surveillance is less well-established, such as local hospitals throughout China.

Keywords: China; RSV-A; RSV-B; children; epidemiology; etiology; pediatric population; pneumonia; respiratory infections; respiratory syncytial virus; season; seasonality; temporal trends; viruses.

Figure 1

Cases of pneumonia and RSV infection in hospitalized children 28 days–13 years of age, by month, Beijing, China, July 1, 2007–June 30, 2015. A) Cases of pneumonia (defined as International Classification of Diseases, 9th Revision, codes 480–488), including children not enrolled in the study (n = 9,950). B) RSV-positive cases (n = 1,270), by subgroup. The shaded area represents the total number of children enrolled in study (n = 4,225). The horizontal ribbon on top of the chart denotes the dominant RSV subgroup for that year. We assigned 2013–14 as an RSV-B–dominant season for the purposes of modeling, although the numbers of RSV-A and RSV-B cases were almost equal. Orange vertical lines denote the Chinese Spring Festival; dashed vertical lines indicate divisions between seasons. RSV, respiratory syncytial virus; RSV-A, RSV subgroup A; RSV-B, RSV subgroup B.

Figure 2

Hospitalized children with pneumonia testing positive for RSV, by age group, calendar season, and RSV subgroup, Beijing, China, July 1, 2007–June 30, 2015. A) Number of RSV-positive children (indicated by numbers above bars) by age group and season. Summer is defined as June–August, autumn as September–November, winter as December–February, and spring as March–May. B) Percentage of infants aged 28 days–5 months positive for RSV, by RSV season. The horizontal ribbon on top of the chart denotes the dominant RSV subgroup for that season. We assigned 2013–14 as an RSV-B–dominant season for the purposes of modeling, although the numbers of RSV-A and RSV-B cases were almost equal. Dashed line indicates 50% positivity. C) Percentage of infants 28 days–5 months of age positive for RSV, by RSV subgroup. RSV, respiratory syncytial virus; RSV-A, RSV subgroup A; RSV-B, RSV subgroup B.

Figure 3

Average percentage of PCR tests positive for respiratory syncytial virus (RSV) per week among hospitalized children 28 days–13 years of age with pneumonia, Beijing, China, July 1, 2007–June 30, 2015. Graph begins at calendar week 27. A seasonal curve is superimposed onto the graph. RSV season was defined as consecutive weeks during which the percentage of RSV-specific PCRs testing positive per week exceeded a 10% threshold. Season onset and offset are indicated by the 2 orange vertical lines.

Figure 4

RSV season duration and peak, by year, Beijing, China, July 1, 2007–June 30, 2015. RSV season was defined as consecutive weeks during which the percentage of RSV-specific PCRs testing positive per week exceeded a 10% threshold. Graph begins at calendar week 27. *We assigned 2013–14 as an RSV-B–dominant season for modeling purposes, although almost equal numbers of RSV-A and RSV-B were identified that season. RSV, respiratory syncytial virus; RSV-A, RSV subgroup A; RSV-B, RSV subgroup B.

Figure 5

Analysis of nonlinear influence of age and RSV year on RSV activity among children 28 days–13 years of age hospitalized with RSV infection, Beijing, China, July 1, 2007–June 30, 2015. Graphs show effect of age (A) and RSV season (B) on probability of infection (p<0.001 for both). The rug plot along the x axis shows the observed values; gray shading indicates 95% CIs. RSV, respiratory syncytial virus.