Newly infected AIDS patients rarely know they have the virus and can continue their high-risk behavior just when they are the most infectious, Dutch researchers reported.

They said the case of a man freshly infected with the AIDS virus demonstrated the dangers of relying on quick HIV tests if patients have flu-like symptoms.

The 49-year-old man tested negative at an Amsterdam clinic using a standard quick test for the virus, but more sophisticated, time-consuming tests later showed the patient in fact did have a large amount of HIV in his blood, Henry de Vries of the University of Amsterdam and colleagues reported.

“Recent infections are characterized by a highly infectious phase and, if gone unnoticed, can have a large contribution to the ongoing transmission of HIV,” De Vries and colleagues wrote in the online journal Eurosurveillance.

“Healthcare providers should be aware of primary HIV infection and the pitfalls in its diagnosis.”

People often have symptoms days after they get HIV, but they are usually mild and look like any number of other infections.

This man had “fever, malaise, generalised rash, anal itching and rectal discharge after unprotected receptive anal and oral intercourse with an anonymous partner in a gay cinema one week before,” the researchers wrote.

He had a number of sexually transmitted infections, including gonorrhea and chlamydia, but the quick HIV test came back negative.

Other HIV tests were not conclusive, but a genetic test called an immunoblot assay confirmed the AIDS infection two weeks later.

In addition, the infection can damage the delicate skin of the vagina, anus and penis, making transmission even more likely.

SOURCE: Eurosurveillance, online December 3, 2009.