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

Background: 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. Methods: 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 (11:8 to 1:256) was challenged against 100 tissue culture infective doses of the three Sabin strains. Titers > 1:8 were considered to be protective. Results: 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. Conclusions: 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.