Transmission of Respiratory Syncytial Virus Among Children Under 5 Years in Households of Rural Communities, the Philippines

Otomaru, Hirono; Kamigaki, Taro; Tamaki, Raita; Okamoto, Michiko; Alday, Portia Parian; Tan, Alvin Gue; Manalo, Joanna Ina; Segubre-Mercado, Edelwisa; Inobaya, Marianette Tawat; Tallo, Veronica; Lupisan, Socorro; Oshitani, Hitoshi

This study had several limitations. First, we did not collect specimens for RSV testing from all RSV-ARI cases. We considered episodes that occurred in the same household within 10 days before and after onset of a confirmed case as possible RSV-ARI cases, which might have overestimated RSV transmission among children in the household. Second, we did not consider asymptomatic cases in our analysis. A previous study has reported that 17.3% of RSV infections are asymptomatic among children <5 years old and that these asymptomatic cases play an important role as a source of transmission [31] . Third, since we collected the data of ARI episodes and clinical specimen only from children <5 years old, we could not capture the entire picture of household RSV transmission. In total, there was no possible index case for approximately 70% (44 of 62) of the young infants with RSV. A previous study has shown that parents and school-age children also play an important role as a source of RSV infection for infants [13] . Moreover, we could estimate R 0 by using the cases <5 years old. There might be a secondary case infected by children <5 years old. Therefore, R 0 in our analysis might be underestimated, and further study is warranted to understand RSV transmissibility among entire population including ≥5 years old. Fourth, we did not consider RSV transmission from outside the household. For example, contact with playmates and other infants in a day care center might be an important source of infection for infants. It is possible that they acquired RSV infection outside of the household. However, we could not analyze this possibility due to the study design. More detailed epidemiological studies, including social network analysis, are required to understand the complete RSV transmission dynamics. Despite these limitations, we managed to gain insight into RSV transmission patterns in a household, especially for young infants. We also estimated epidemiological parameters, such as the serial interval and R 0 . We believe that accumulation of such data in different settings will help establish more effective control measures against RSV in the future.