The relationship of meteorological conditions to the epidemic activity of respiratory syncytial virus

Abstract

Our aim was to obtain knowledge of how meteorological conditions affect community epidemics of respiratory syncytial virus (RSV) infection. To this end we recorded year-round RSV activity in nine cities that differ markedly in geographic location and climate. We correlated local weather conditions with weekly or monthly RSV cases. We reviewed similar reports from other areas varying in climate. Weekly RSV activity was related to temperature in a bimodal fashion, with peaks of activity at temperatures above 24-30 degrees C and at 2-6 degrees C. RSV activity was also greatest at 45-65% relative humidity. RSV activity was inversely related to UVB radiance at three sites where this could be tested. At sites with persistently warm temperatures and high humidity, RSV activity was continuous throughout the year, peaking in summer and early autumn. In temperate climates, RSV activity was maximal during winter, correlating with lower temperatures. In areas where temperatures remained colder throughout the year, RSV activity again became nearly continuous. Community activity of RSV is substantial when both ambient temperatures and absolute humidity are very high, perhaps reflecting greater stability of RSV in aerosols. Transmission of RSV in cooler climates is inversely related to temperature possibly as a result of increased stability of the virus in secretions in the colder environment. UVB radiation may inactivate virus in the environment, or influence susceptibility to RSV by altering host resistance.

Fig. 1

Total number of respiratory syncytial virus (RSV) cases identified throughout several years of observation in six North American cities. The horizontal axis represents weeks 1–52 for five cities, and months 1–12 for Bethel, AK (only monthly RSV totals were available from Bethel). The vertical axis displays the number of RSV cases identified during each year of surveillance at each site. Each circle represents the total number of RSV cases identified in each week (or, in the case of Bethel, each month) for each year surveyed.

Fig. 2

Total number of respiratory syncytial virus (RSV) cases identified throughout several years of surveillance in Mexico City, Delhi, India, and Santiago, Chile. The horizontal axis represents months 1–12 for each site (only monthly RSV totals were available). The vertical axis displays the number of RSV cases identified during each year of surveillance at each site. Each circle represents the total number of RSV cases identified in each month of each year surveyed.

Fig. 3

Relationship of mean temperature to respiratory syncytial virus (RSV) activity in five North American cities. The vertical axis reflects the number of RSV cases identified each week during each year of surveillance at the five study sites that provided weekly RSV totals. The horizontal axis represents the weekly average of mean daily temperatures recorded at intervals corresponding to those for which RSV totals were available. Both linear and curvilinear correlations were calculated (linear r=0·135, P=0·036; curvilinear r=0·218, P=0·021).

Fig. 4

Relationship of relative humidity to respiratory syncytial virus (RSV) activity in five North American cities. The vertical axis reflects the number of RSV cases identified each week during each year of surveillance at the five study sites that provided weekly RSV totals. The horizontal axis represents the weekly average of mean daily relative humidity (percent) recorded at intervals corresponding to those for which RSV totals were available (r=0·24, P=0·11).