Prevalence of anti-poliovirus type 1, 2 and 3 antibodies in unvaccinated Italian travelers.

Abstract

Immunization against poliomyelitis is recommended for international travelers to developing countries. However, the level of antibodies varies even in previously unvaccinated persons, due to wild-type or vaccine-type infections in the eldest travelers. In 1999, we conducted a seroprevalence study in the Lombardy region (northern Italy), using sera collected in 1994 from a population aged 50 to 59 years. The study subjects were consecutive, randomly selected travelers enrolled in an anti-hepatitis A virus antibody study. Neutralizing antibodies were titrated on Vero cells in microtiter plates. Each serum dilution (1:8 to 1:256) was challenged against 100 tissue culture infective doses of the three Sabin strains. Titers> 1:8 were considered to be protective. We studied 98 travelers, 59 male and 39 female, of mean age 54 years. Seventy-three (74.4%) reported previous travel abroad, but none had been vaccinated against polio. Dietary habits included consumption of seafood in 74.4% and raw vegetables from their own garden in 52.1%. The seroprevalences for neutralizing antibodies against poliovirus type 1, type 2 and type 3 were 86.7%, 89.9%, and 86.7%, respectively. All travelers presented protective antibody titers against at least one of the three viral types. Protective antibody titers were unrelated to travel history or dietary habit. A high proportion of the previously unvaccinated adults in our sample presented protective immunity to polioviruses. This observation may have implications for cost-effectiveness analysis of generalized polio vaccination in adult Italian travelers.