Every year, in the Obstetrics Hospital St. Anna of Turin, Italy, about 5500 women give birth. This represents 2/3 of the infants born in Turin.
In 1990 and 1991, from April to June, anonymous blood specimens were collected from the first 1000 newborn with no known risk factor for HIV. Mothers known to be H1V seropositive and/or drug abusers at time of admission were not included in the population from which specimens were collected.
Samples blotted and dried onto filter-paper for phenylketonuria and hypothyroidism screening were sent to the Department of Hygiene and Community Medicine. After processing according to Holt (1), testing for HIV antibodies was carried out with E.L.I.S.A. (ETI-HTLVIII-K-eia Sorin Biomedica).
10 samples out of 1000 (year 1990) and 20 out 1000 (year 1991) were positive for HIV antibodies. The same E.L.I.S.A. was repeated and resulted positive for 5 out of 10 (1990) and 5 out of 20 (1991). Western blot, carried out with Biotech/DuPont HTLVIII, confirmed positivity in 1 out of 5 (1990) and none out of 5 (1991).
The specificity of ELISA, using the Western blot as a reference, was 99.50/0 (9 false positive).
The reagent cost resulted about italian liras (IL) 7000 per sample, higher than the different systems used in other studies (2). This cost can be attributed both to the cost of the reagent ELISA (IL 6500 per sample) and to the need of repeating and confu'ming the samples positive at the first screening (29 false positives).
This monitoring approach, although the predictivity of positive results is poor in low prevalence conditions, seems to provide a sensitive and practical epidemiologic indicator in population with no known risk factors for HIV. It allows the HIV prevalence in the sexually active heterosexual individuals in Turin to be estimated, and suggests that heterosexual transmission has not increased in a one year period (1990)(1991).
Certainly, if adopted, the cheaper diagnostic methods, as in (2) (3), would improve costeffectiveness.