Incidence of common respiratory viral infections related to climate factors in hospitalized children in Hong Kong

Abstract

Hong Kong has a subtropical climate and an influenza seasonality lying approximately mid-way (March-June) between those of the Northern (November-March) and Southern (June-September) hemispheres. Respiratory syncytial virus (RSV) shares a similar seasonality to that of influenza in Hong Kong and is another important respiratory infection of childhood. Daily virus incidence data from public hospitals in Hong Kong's New Territory East Cluster, together with Hong Kong climate data were obtained for 2000-2007. Statistical time-series analysis using monthly time windows showed that influenza A and RSV incidence increased with higher environmental relative humidity, whereas influenza B incidence decreased with higher environmental temperatures. The other climate variables (including vapour pressure as a measure of absolute humidity) were not significantly related to the incidence of these respiratory viruses. Data from this study further reinforces the concept that the relationship between climate factors and respiratory virus incidence differ between subtropical/tropical and temperate countries.

Sunshine, rainfall, humidity and child pneumonia in the tropics: time-series analyses

“…In tropical settings lower respiratory infections in children are generally found to be more common during periods of higher rainfall and humidity, consistent with our results [7][8][9][10][11] . Rainfall is not convincingly associated with pneumonia incidence in time series studies from temperate settings 10,12,13 .…”

“…Low sunlight and temperature are consistently associated with high pneumonia incidence in time series studies in temperate settings, where annual peaks of lower respiratory infections occur during the short days of winter 10,[12][13][14][15][16] . The association between temperature and respiratory infections in children is inconsistent in time series studies from tropical settings, suggesting temperature is unlikely to be an important driver of pneumonia incidence in the tropics [6][7][8][9][10][11] . Less evidence examining the association of respiratory infection and sunlight exists from tropical settings.…”

“…Respiratory syncytial virus (RSV) infections were positively correlated with the number of rainy days and relative humidity in Indonesia and Malaysia, positively correlated with relative humidity and dew point in Mexico, and positively correlated with relative humidity in Hong Kong, although in Singapore a negative correlation with relative humidity was found [6][7][8][9][10][11] . In temperate settings where pneumonia peaks in winter, time series analyses have consistently found peaks of RSV and invasive pneumococcal disease (IPD) to be inversely correlated with temperature and daylight hours 10,[12][13][14][15][16] .…”

Ecological factors associated with pandemic influenza A (H1N1) hospitalization rates in California, USA: a geospatial analysis

“…First, each of the socioeconomic variables including population proportions of high school graduates (aged >25 years), percentage of persons living in poverty, and median household income were not significantly related to hospitalization rates. Second, mean county temperatures and dew point temperatures were not significantly related to hospitalization rates, which is inconsistent with other studies claiming that host immune responses are adversely sensitive to cold and dry climates (Lowen et al 2007;Tang et al, 2010). Finally, all race/ethnicity variables were not significantly related to county hospitalization rates, which is inconsistent with the majority of hospitalizations being Hispanic at the individual level.…”

“…Since many influenza studies have found climatic factors to be related to influenza transmission (see Tang et al, 2010), it would be reasonable to consider climatic effects in human influenza transmission rates. Therefore, climatic variables were included using county mean temperatures and mean dew point temperatures (°C) constructed by averaging each county's weather station records between the months of April and September 2009 obtained via the Prism Climate Group.…”