A negative test is valid only if the person did not have any exposure in past three months, counted backward from the test date. Higher the viral load, higher the risk.Viral load is very high during the initial weeks when our immune system has not started producing antibodies. It certainly does not mean that affected perople are less infectious afterwards. A positive person can transmit the virus anytime if the conditions of transmission prevail.
However people generally do not got for a test after a couple of weeks of their exposure, therefore I am unable to understand why you doubt anyone's results.
Thanks for the reply diver. My concern was mainly if I have sex with a partner who has tested for HIV negative but might have contracted the virus a week or two ago, then am i at risk. Cuz as per your reply this is the time viral load is high and this is teh time when i am at most risk.
That is the reason, condom protection is always recommended for anyone, outside your mutually committed long term partnership.