The September epidemic of asthma hospitalization: School children as disease vectors

Viral infections are associated with the majority of asthma exacerbations in children and adults. Increased asthma hospitalization rates of children and adults, particularly in the early fall, have been observed to follow school vacations. We sought to determine the sequence of timing of September asthma hospitalization epidemics in children and adults and to determine whether school-age children are the primary source of transmission of agents that cause them. By using Canadian asthma hospital admission data from 1990 to 2002, we examined geographic variation in the timing of fall asthma epidemics and applied mathematical modeling to estimate their exact timing and magnitude in school-age children, preschool children, and adults, and relation to school return. The September asthma hospitalization epidemic peak occurred in school-age children each year on average 17.7 (95% CI, 16.8-18.5) days after Labor Day. Similar epidemics of lesser magnitude were observed in preschool children peaking 1.7 (95% CI, 0.9-2.5; P < .001) days later, and in adults 6.3 (95% CI, 4.7-7.9; P < .001) days later than in school-age children. The epidemics peaked 4.2 (95% CI, 1.2-7.1; P < .001) days earlier in school-age children in northernmost compared with southernmost latitudes. September epidemics of asthma hospitalizations in Canada have a precise relationship to school return after the summer vacation. It may be speculated that school-age children transmit the agents responsible for the epidemic to adults. Measures to improve asthma control and reduce transmission of infections should be directed at children with asthma before school return.