Risk factors and patterns of household clusters of respiratory viruses in rural Nepal

Scott, E. M.; Magaret, A.; Kuypers, J.; Tielsch, J. M.; Katz, J.; Khatry, S. K.; Stewart, L.; Shrestha, L.; LeClerq, S. C.; Englund, J. A.; Chu, H. Y.

Our finding that preschool-age children, rather than schoolage children, are most likely to transmit non-influenza respiratory viruses is likely due to differences in study sample and design, as well as transmission patterns. Households in our study experienced fewer respiratory viral illness episodes than reported in other household studies that included asymptomatic viral detections [5, 7, 15] . In a study of respiratory virus-positive influenzalike illness in households in Vietnam, households experienced 1.6 illness episodes over a 1-year period (including influenza and bocavirus), whereas we found a mean of 1.4 illness episodes per household [8] . Our surveillance sample includes a higher proportion of young children aged 0-4 years, including study infants, relative to the overall proportion in the Sarlahi district of Nepal (32.4% vs. 11.3%) and a lower proportion of children aged 5-14 years (11.6% vs. 27.9%) [18] . It is possible that the true transmitting cases were absent during the weekly household visit or asymptomatic according to our criteria, though this is less likely for younger children who have median viral shedding duration of longer than 1 week [31] . We likely did not capture the full a Total for initial episodes, transmission episodes and transmission events are less than the sum of columns as infections with coinfections were counted a single initial infection in total. Similarly, the total for index cases may be less than the sum of columns as coinfection transmission or transmission to multiple household members was only counted once in total. b Median serial index was defined as the median number of days between symptom onset of index and secondary case.