The Seattle virus watch. V. Epidemiologic observations of rhinovirus infections, 1965-1969, in families with young children.

Rhinovirus (RV) infections in Seattle Virus Watch (VW) families (1965-1969) were monitored by screening respiratory specimens in WI-38 cell cultures and by homotypic neutralization tests on sera related to family episodes revealed by RV isolation. Temporally related illness in members not proven infected was also taken to indicate infection. RV isolates (including those from the New York VW, 1961-1965) were typed within the official 90-serotype frame. Typed isolates from New York (165 with 39 serotypes) and Seattle (456 with 59 serotypes) were compared with the Tecumseh Study to test the hypothesis that some serotypes are "common," persisting because of greater infectivity. Of 32 serotypes qualifying as "common" in at least 1 study, 4 were "common" in all 3 studies and 8 in 2 studies. The 23 "common" Seattle serotypes differed from the remaining 36 serotypes in being more infective and in their more frequent association with prolonged shedding. The New York and Seattle isolates together revealed an increase over time in the proportion not typable or of of higher numbered types, consistent with progressive shift in RV antigenic character. WI-38 isolates indicated spring peaks of RV all 4 years but a fall peak only in 1967. An even larger fall peak was seen when all specimens from September-November 1968 were re-examined in fetal tonsil diploid cells. Thus, both spring and fall peaks appear to describe RV seasonality. RV infections explained 16% of all reported respiratory illness (20% of upper respiratory), but RV-associated illness in young children, especially under 2 years, was more severe and almost twice as frequent as in adults. The age of introducers and the direct relation of family size to frequency of episodes indicate that community spread depends largely on preschool children, including infants. Within families, the secondary attack rate (SAR) was highest following paternal introduction and, for all introducers, the SAR varied inversely with age (mother excepted). RV shedding was observed most often (85% of specimens) from the day before to 6 days after illness onset but prolonged shedding was common (to 21 days in 20% and 28 days in 1.4% of infections). RV infectivity, reflected by SAR among nonimmunes, was highest for infants (78%) and, for all ages, was greater with ill than with well introducers (71% versus 27%). Immunogenicity of RV was poor (Seroresponse: 48% of shedders, 32% of nonshedding contacts) but varied greatly with serotype. Illness frequencies among non-immunes were 59% for all proven infections and 35% when infection was not shown..