*Reiseklinikken-Oslo Travel Clinic, St Olavs
plass 3 N-0165 Oslo, Norway.
E-mail: hasle@reiseklinikken.com; annegrete.skar@ulleval.no; jon.Pedersen@fafo.no
361 subjects who have lived for a period in a highly endemic country for hepatitis A were tested for hepatitis A IgG to determine the need for hepatitis A vaccination. Hepatitis A IgG testing on this indication is probably cost effective when there is more than 30-40% chance of being positive. In our sample 80% of the subjects were found hepatitis A IgG positive. When the a priori chance of immunity is low the vaccine should be given without testing, and when the a priori chance of being positive is very high the vaccine should be omitted.
Using proportional hazards regression for current status data we have estimated the risk of acquiring hepatitis A in different regions. The calculation was based on the start and end times of their stay in the endemic country, a history of jaundice was rarely present. The start time was most often the year of birth. After 5 years of residence in an endemic country there was only 23 percent chance of testing negative for the hepatitis A IgG. In our material 96% of people who had lived more than ten years in Africa South of Sahara or in Pakistan had natural immunity.
It seems justifiable to recommend African and Pakistani people to travel without hepatitis A vaccination, even when there is no time to wait for the test result. As the cost of vaccination is a great issue for many immigrants visiting their home country these findings have an important practical benefit.