When are patients infected with HIV most contagious?

Posted by Abigail Place • May 20th, 2011, The New England Journal of Medicine:

There are now 33.2 million people living with human immunodeficiency type 1 (HIV-1) infection, and 2.6 million additional cases are diagnosed each year. The need for effective HIV-1 prevention has never been greater.

Clinical Pearls

• How quickly after exposure can HIV infection be detected?

Immediately after exposure and transmission, as HIV-1 is replicating in the mucosa, submucosa, and draining lymphoreticular tissues, the virus cannot be detected in plasma; this so-called eclipse phase generally lasts 7 to 21 days. The stages that define acute and early HIV-1 infection are characterized by the sequential appearance of viral markers and antibodies in the blood. More sensitive, fourth-generation tests, which detect both antigens and antibodies, shrink the virus-positive-antibody-negative window by about 5 days. Testing for viral RNA in plasma closes this gap by an additional 7 days.

• When are patients infected with HIV most contagious?

The per-person probability of transmitting HIV-1 is most closely correlated with the viral burden in blood; each time the viral burden in an HIV-1-infected person increases by a factor of 10, the risk of transmission is expected to increase by a factor of 2.5. The risk of contagion from patients with acute, early infection appears to be much higher than that from patients with established infection, at least in part because of the high viral load and the homogeneity of viral variants clearly capable of causing infection. Read more>>