Most doctors will tell you that monthly testing is probably unnecessary, because the incubation period for HIV is longer than that (usually three months). Also, even if an SP becomes HIV-positive at some point during the three-month window, the chances of the SP spreading HIV to clients still remains quite low (assuming safer sex practices are followed) because of the very small viral load. The risk of seroconversion for sexual partners is related to the person's viral load, so if someone has only recently acquired HIV, they aren't as likely to transmit it to others.
A "very small viral load" & not as "likely to transmit {HIV} to others" in the first three months after becoming HIV positive?
"The phase of infection. HIV is much more contagious in the acute infection phase (first eight to 12 weeks after infection) as well as in the final phases when advanced disease (or Aids) has set in. The reason why HIV is easier transmitted during these phases, is because the viral load is especially high in the acute infection phase, and again in the final phase of Aids."
http://www.health.am/aids/more/transmission_through_sexual_acts/
"During this period (usually 2–4 weeks post-exposure) most individuals (80 to 90%) develop an influenza or mononucleosis-like illness called acute HIV infection, the most common symptoms of which may include fever, lymphadenopathy, pharyngitis, rash, myalgia, malaise, mouth and esophageal sores, and may also include, but less commonly, headache, nausea and vomiting, enlarged liver/spleen, weight loss, thrush, and neurological symptoms. Infected individuals may experience all, some, or none of these symptoms. The duration of symptoms varies, averaging 28 days and usually lasting at least a week.[27]
"Because of the nonspecific nature of these symptoms, they are often not recognized as signs of HIV infection. Even if patients go to their doctors or a hospital, they will often be misdiagnosed as having one of the more common infectious diseases with the same symptoms. As a consequence, these primary symptoms are not used to diagnose HIV infection, as they do not develop in all cases and because many are caused by other more common diseases. However, recognizing the syndrome can be important because the patient is much more infectious during this period.[28]
http://en.wikipedia.org/wiki/HIV
"The window period for a test is the amount of time from the initial infection event until the disease can be detected.[17] Exposure to HIV, followed by replication of the virus, may take as long as six months to reach a level detectable in many testing methods. An HIV antibody test usually detects the HIV antibodies within two to eight weeks, but can have a valid negative result for a long as 2 to 6 months after initial infection. Viral load tests can also be used to diagnose HIV infection, especially in children under 18 months born to mothers with HIV, where the presence of maternal antibodies prevents the use of antibody-based (ELISA) diagnostic tests.[18]
"On June 15th 2010, the FDA approved the first diagnostic test capable of detecting HIV antigens and HIV antibodies. Use of the Abbott ARCHITECT HIV Ag/Ab combo test can reduce the window period to 20 days.[19] This diagnostic test can be used during the acute phase, when the immune system is still developing antibodies and the virus is replicating unchecked. A person, who may be unaware of the infection, is highly infectious during this time yet may test negative for HIV using tests that detect anti-HIV antibodies only.
http://en.wikipedia.org/wiki/Viral_load
