In the very early years of HIV testing the presence of antibodies to malaria was thought to lead to false positive results (Biggar). The tests had originally been designed without taking into account the prevalence of malarial antibody in populations different from the United States, where the tests were first developed. By 1991, a study using newer antibody test kits failed to demonstrate any difference in prevalence of malarial antibody between seropositive and seronegative blood donors in an equatorial country, suggesting that people with malarial antibodies are now no more likely to test positive for HIV antibodies (Chattopadhya).