A serological method for demonstrating recent infection by rubella virus.

or even inapparently, diagnosis on clinical grounds alone is liable to error. Because of the risk of subsequent congenital malformations (Gregg, 1941), serological tests are particularly valuable in the assessment of mothers exposed to or acquiring rubella early in pregnancy. Both neutralizing and haemagglutination-inhibiting (H.I.) antibodies often rise sharply to a high level early in the disease, a significant level of H.I. antibody sometimes being present on the first day of rash (Stewart et al., 1967; A. Field, personal communication). In our experience many patients with rubella, particularly those who are pregnant, may be five to seven days or more from the onset of symptoms by the time they are referred for investigation. In these circumstances there may not be a significant rise in antibody titre between an acute phase sample of serum and a subsequent one taken two to three weeks later, both having equally elevated titres. This makes it impossible to say whether their antibody results from recent or from past infection. Although a rising or high complement-fixing antibody titre is useful, since it suggests relatively recent infection (Sever et at., 1965; Schmidt and Lennette, 1966), a significant rise in antibody titre may not become detectable until four to six weeks after onset of symptoms (Sever et al., 1966; Banatvala, unpublished observations), peak titres sometimes being achieved as late as three to six months after infection (Veronelli and Eckert, 1966).