Human immunodeficiency virus (HIV) infection: Clinical sciences

Human immunodeficiency virus, or HIV for short, is a single-stranded RNA retrovirus that targets the body’s immune system. HIV is transmitted by contact with infected body fluids, such as blood, semen, and vaginal fluids. There are two types of HIV: HIV-1 and HIV-2; but generally, when we talk about HIV infection, we usually mean HIV-1 because it's the most widespread.

Now, HIV causes immunosuppression by targeting and infecting CD4 T cells, which are a type of white blood cell that helps coordinate the immune response to infection. The acute phase of HIV infection is called acute retroviral syndrome, after which the individual can be asymptomatic for as long as a couple of years. However, without appropriate medical management, HIV infection can progress to acquired immunodeficiency syndrome, or AIDS.

Now, if your patient presents with chief concerns suggesting an HIV infection, first perform a focused history and physical examination. These patients typically have nonspecific symptoms, such as fever, fatigue, night sweats and unintentional weight loss. Additionally, your patient might report myalgias, arthralgias, or gastrointestinal manifestations, like nausea, vomiting, and diarrhea. Your patient could also report a sore throat.

Other historical findings may include high-risk sexual behavior such as unprotected sexual activities or multiple sexual partners; intravenous substance use; or occupational risk factors such as accidental needlestick injury.

Physical examination might reveal a rash, lymphadenopathy, or signs of sexually transmitted infections, such as purulent urethral discharge or painful fluid-filled blisters around the genitals. You might also find needle marks on the skin overlying veins in individuals who have used intravenous drugs. Finally, distinctive but rare manifestations of HIV infection include mucocutaneous ulcers, which typically affect oral and genital regions.

Here’s a clinical pearl! In some cases, patients with undiagnosed HIV infection may present with opportunistic infections like Pneumocystis jirovecii pneumonia, or opportunistic neoplasms, such as Kaposi sarcoma, which presents as dark, reddish-purple or brown skin lesions. Unfortunately, these are also considered AIDS-defining illnesses, which occur at a CD4 count less than 200 per microliter. So, if you encounter a patient with an opportunistic disease, without a known immunocompromising condition, remember to perform HIV testing!

With these findings, you should suspect an HIV infection, and order a combined HIV antibody and p24 antigen immunoassay.

Here’s a clinical pearl to keep in mind! It’s also recommended to screen for HIV during pre-pregnancy planning and as early in pregnancy as possible. Individuals with certain risk factors, such as more than one sexual partner, should be screened more often.

Okay, first let’s focus on patients with a non-reactive HIV antibody and p24 antigen immunoassay. This means both HIV antibodies and p24 antigen were not detected. Your next step is to assess for HIV exposure within the past month. If your patient reports no known recent HIV exposure, you can exclude HIV infection and consider an alternative diagnosis.

On the other hand, if your patient reports a known HIV exposure, order an HIV-1 nucleic acid test, or HIV-1 NAT for short, which detects levels of HIV-1 RNA in the blood. This test can help you rule out HIV infection because HIV antibodies and the p24 antigen can take up to 6 weeks to appear in the blood and be detected, while the NAT can usually detect HIV 10 to 33 days after exposure! So, if the HIV-1 NAT is negative, you should consider an alternative diagnosis. However, if the HIV-1 NAT is positive, diagnose HIV-1 infection.