Possible association of influenza A with fetal loss: investigation of a cluster of spontaneous abortions and stillbirths.

It has been suspected that influenza infection is associated with fetal or perinatal mortality, but little recent evidence supports this hypothesis. A small cluster of early and late fetal deaths in early 1986 prompted an epidemiological investigation. Women whose pregnancies were affected (cases) were compared with women whose pregnancies had a normal outcome (controls). Case pregnancies were distinguished by a significant excess of recent flu-like illness (p = 0.006), and were significantly more likely than controls to have serological evidence of influenza A infection (p = 0.00067), predominantly the influenza A H3N2, Christchurch/4/85-like strain. The cluster was recognised because most cases were patients of one health centre. Larger epidemiological studies will be needed to confirm an association between influenza A and fetal death, but this cluster suggests that influenza A may have an adverse influence on fetal survival.