One in five adults in New York are putting themselves at risk of HIV by having sex with multiple partners or using needles to inject drugs, a study by the US Health Department stated.
Around 92 per cent of them do not think they are at risk, the study found.
The survey also found that out of the people with multiple sex partners, almost 60 per cent put themselves at risk by not always using condoms.
Compared to the national data, sexual risk-taking appears to be more common among New York City adults, but injection drug use appears to be roughly the same.
The findings highlight common misperceptions about HIV and underscore the importance of education and routine HIV testing.
"Far too many people are in danger of contracting HIV through risky behaviour," Dr Thomas R Frieden, Health Commissioner for New York City, said.
"Reducing the number of sex partners and protecting yourself and your partners by consistently using condoms will help you stay safe. We should all know our HIV status, regardless of whether we think we're at risk and health care providers should offer this test to their patients," he said.
The study, whose lead author is Trang Nguyen, is the first in a US to use a citywide survey of blood samples to estimate HIV prevalence.
The findings suggest that approximately 1.4 per cent of New York City adults are infected with HIV, about the same proportion that past studies have obtained by pooling case reports from hospitals, clinics and doctors' offices. (MORE)
The rate of those infected by HIV in New York City is nearly four times the national rate (0.37 per cent) and is a likely reflection of a larger population of ethnic minorities and men who have sex with men, the study found.
Keeping with past surveys, the new study found an especially large HIV burden among men who have sex with other men. Their infection rate was 14 per cent, approximately 38 times the citywide average.
Black and Hispanic New Yorkers have long been disproportionately affected by the HIV epidemic. Indeed, this survey showed that rates of HIV are nearly six times higher among black New Yorkers than white New Yorkers (3.3 versus 0.6 per cent), a trend that has been documented through other surveillance methods since the early 1980s.
The HIV rate among Hispanic New Yorkers (1.3 per cent) was more than twice that of whites. While HIV infection due to injection drug use has declined in New York City since the 1990s, the new study suggests the disease is still common among needle users, 21 per cent of whom have tested positive for HIV.
"If you are using drugs, get help to stop," added Frieden. "But protect yourself until you stop by not sharing equipment."
To reduce risky sexual behaviour, the Health Department is planning an educational campaign targeting men who have sex with men. The agency also distributes more than three million branded NYC condoms each month.
To reduce transmission among drug users, the US Health Department sponsors needle-exchange programmes in several boroughs, helps health care providers get their patients off drugs, and contracts with service organisations to provide treatment for addiction.