HIV transmission and seroconversion

Last edited 02/2018 and last reviewed 07/2023

HIV infects a patient during sexual contact or by intravenous administration.

• sexual transmission may occur during heterosexual or homosexual intercourse
• body fluids, such as semen, containing HIV come into contact with mucosal surfaces
• HIV binds to and infects local CD4 positive cells, predominantly macrophages.
• intravenous administration during blood transfusion delivers a high dose of virus resulting in a poor prognosis. Intravenous drug abuse is a major cause of HIV infection.

During the first few weeks after the initial infection with HIV, majority of patients (40-90%) will develop symptoms consistent with an acute infection. This acute illness associated with HIV seroconversion is known as acute HIV infection (or primary HIV infection, acute retroviral syndrome, seroconversion illness) (1,2).

• usually occurs between 10 days and 6 weeks (timing and duration may vary)
• HIV RNA levels peak, before declining over subsequent weeks
• antibodies to HIV usually develop within 3-5 weeks of becoming infected. The time period between becoming infected and developing antibodies is referred to as the serological “window period” (4)

The risk of onward transmission is particularly high during primary HIV infection (PHI), as individuals have a high viral load but are often unaware they have HIV and may even test antibody negative (5)

Although many patients are symptomatic and seek medical care during PHI, even a very HIV-aware doctor is likely to miss some patients with PHI due to the mild and non-specific nature of the symptoms. Diagnosis of PHI is valuable since this provides an opportunity to

• prevent onward transmission of the disease since patients are more infectious at this stage
• prevent diagnosis at a later stage when there is advanced immunosuppression and the prognosis for the patient is likely to be much worse
• initiate antiretroviral therapy since there is evidence that treatment may be particularly protective at this stage (1)

Reference:

• (1) Chu C, Selwyn PA. Diagnosis and initial management of acute HIV infection. Am Fam Physician. 2010;81(10):1239-44. 
• (2) Griswold J, Tungsiripat M. HIV for primary care physician. Cleveland clinic, Center for continuing education 2017
• (3) The Medical Foundation for AIDS & Sexual Health (MedFASH) 2016. HIV in primary care. A practical guide for primary healthcare professionals in Europe.  
• (4) Health Protection Surveillance Centre (HPSC) 2016. Guidelines for the Emergency Management of Injuries and Post-Exposure Prophylaxis (PEP)  
• (5) The Medical Foundation for AIDS & Sexual Health (MedFASH) 2016. HIV for non-HIV specialists. Diagnosing the undiagnosed