Synergistic effect of passive smoking and artificial feeding on hospitalization for respiratory illness in early childhood.

The synergism of passive smoking and artificial feeding on hospitalization for respiratory illness in early childhood was examined among 2,227 subjects born in the last quarter of 1983 in Chang-Ning District, Shanghai, People's Republic of China. The eligible families were visited by the trained interviewers. A loglinear model shows no interaction on a multiplicative scale between these two factors on the frequency of hospitalization for respiratory illness during the first 18 months of life. However, the synergism of passive smoking and artificial feeding on the consequence was detected by using Rothman's approach that these two synergistic agents worked together producing a detrimental effect much more than that expected by their separate actions. These data suggested that it is more important to stop smoking in the families where the infants were artificially fed.