Use of seasonal influenza virus titer and respiratory symptom score to estimate effective human contact rates

Background: We linked viral titers and respiratory symptom scores for seasonal influenza to estimate the effective contact rate among schoolchildren. Methods: We analyzed 274 diary-based questionnaires. In addition, 2 sets of influenza data from published studies were used to investigate the relationship between viral titer, total symptom score, and normalized contact rate in children. Results: The mean number (SD) of contacts for children in grades 7 to 9 ranged from 9.44 ± 8.68 to 11.18 ± 7.98 person -1 day -1; contact behavior was similar across school grades. The mean number of contacts was 5.66 ± 6.23 person -1 day -1 (range, 0 to 44 person -1 day -1) for the age group of 13 to 19 years. Estimated contact age, household size, contact duration, and contact frequency were the variables most strongly associated with total number of contacts. We also found that a reduction in total respiratory symptom scores among infected individuals had a positive correlation with an increase in the normalized contact rate. Conclusions: The relationship between daily virus titer and respiratory symptom score can be used to estimate the effective contact rate in explaining the spread of an airborne transmissible disease. The present findings can be incorporated into population-dynamic models of influenza transmission among schoolchildren.