Seasonal patterns of invasive pneumococcal disease.
Pneumococcal infections increase each winter, a phenomenon that has not been well explained. We conducted population-based active surveillance for all cases of invasive pneumococcal disease in seven states; plotted annualized weekly rates by geographic location, age, and latitude; and assessed correlations by time-series analysis. In all geographic areas, invasive pneumococcal disease exhibited a distinct winter seasonality, including an increase among children in the fall preceding that for adults and a sharp spike in incidence among adults each year between December 24 and January 7. Pneumococcal disease correlated inversely with temperature (r -0.82 with a 1-week lag; p<0.0001), but paradoxically the coldest states had the lowest rates, and no threshold temperature could be identified. The pattern of disease correlated directly with the sinusoidal variations in photoperiod (r +0.85 with a 5-week lag; p<0.0001). Seemingly unrelated seasonal phenomena were also somewhat correlated. The reproducible seasonal patterns in varied geographic locations are consistent with the hypothesis that nationwide seasonal changes such as photoperiod-dependent variation in host susceptibility may underlie pneumococcal seasonality, but caution is indicated in assigning causality as a result of such correlations.
International Emerging Infections Program, Department of Medical Sciences, Ministry of Public Health, Building 2, Tivanon Road, Nonthaburi 11000, Bangkok, Thailand. sdowell@cdc.gov
Scott F
SF
Dowell
Cynthia G
CG
Whitney
Carolyn
C
Wright
Charles E
CE
Rose
Anne
A
Schuchat
D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D004198:Disease Susceptibility; D005260:Female; D006801:Humans; D015994:Incidence; D007223:Infant; D008297:Male; D017440:Photoperiod; D011008:Pneumococcal Infections / Q000453:epidemiology*; D011159:Population Surveillance; D011891:Rain; D012621:Seasons; D013296:Streptococcus pneumoniae; D013696:Temperature; D014481:United States / Q000453:epidemiology