Salmonella Infection

HIV (human immunodeficiency virus) is a retrovirus that infects and progressively depletes CD4 positive T lymphocytes, causing progressive immunodeficiency and, without treatment, susceptibility to a characteristic range of opportunistic infections and malignancies collectively defining acquired immunodeficiency syndrome (AIDS).

Transmission occurs through sexual contact, blood and blood product exposure (including shared injecting equipment), and vertical (mother to child) transmission during pregnancy, delivery, or breastfeeding.

With effective antiretroviral therapy, HIV has been transformed from a uniformly fatal condition into a manageable chronic disease, with near normal life expectancy achievable in patients diagnosed and treated promptly and who maintain good adherence, which underscores the importance of both early diagnosis and sustained engagement in care.

• Acute HIV infection (seroconversion illness), occurring typically 2 to 4 weeks after exposure, presents with a non-specific, often self limiting mononucleosis like illness: fever, lymphadenopathy, pharyngitis, myalgia, and a maculopapular rash, frequently unrecognized or misattributed to a viral illness at the time.
• A prolonged clinically latent period, often lasting many years, follows, during which the patient may be entirely asymptomatic despite ongoing viral replication and gradual CD4 count decline.
• As CD4 count falls, patients become progressively susceptible to a range of characteristic opportunistic infections and conditions, generally occurring at recognized, roughly predictable CD4 thresholds: oral or esophageal candidiasis and reactivation of latent tuberculosis at moderately reduced CD4 counts; Pneumocystis jirovecii pneumonia, cerebral toxoplasmosis, and cryptococcal meningitis at more severely reduced counts (typically below 200 cells per microliter); and cytomegalovirus retinitis, disseminated Mycobacterium avium complex infection, and progressive multifocal leukoencephalopathy at the most severely reduced counts (typically below 50 cells per microliter).
• AIDS defining malignancies include Kaposi sarcoma (associated with human herpesvirus 8 co-infection, presenting with characteristic violaceous skin, mucosal, or visceral lesions), non-Hodgkin lymphoma, and, in women, invasive cervical cancer, reflecting the broader increased malignancy risk associated with chronic immunodeficiency and, for some of these, co-infection with oncogenic viruses.

• Fourth generation combination antigen and antibody testing is the standard initial screening test in most settings, detecting both HIV antibody and p24 antigen, which narrows the diagnostic window period compared to older antibody only assays, since p24 antigen becomes detectable before antibody seroconversion is complete.
• A reactive screening test is confirmed with a supplemental, differentiation assay distinguishing HIV-1 from HIV-2, per standard testing algorithms.
• HIV RNA viral load testing can detect infection during the window period before antibody seroconversion is complete, and is particularly useful when acute HIV infection is clinically suspected despite a negative or indeterminate antibody based test.
• Once diagnosis is confirmed, baseline assessment includes CD4 count (establishing the degree of immunodeficiency and guiding opportunistic infection prophylaxis needs), HIV viral load (establishing a baseline before treatment), genotypic resistance testing (guiding initial antiretroviral regimen selection), and screening for common coinfections, including hepatitis B, hepatitis C, syphilis, and tuberculosis, alongside other routine baseline bloods.

Differentials for the acute seroconversion illness include infectious mononucleosis and other viral illnesses. The differential for specific opportunistic infections and malignancies is addressed within their own respective entries.

• Antiretroviral therapy is now recommended for all patients diagnosed with HIV, regardless of CD4 count, reflecting a shift from older, CD4 threshold based initiation criteria, given clear evidence that early treatment improves individual outcomes and reduces onward transmission risk.
• Modern first line regimens typically combine two nucleoside or nucleotide reverse transcriptase inhibitors with a third agent, most commonly an integrase strand transfer inhibitor (such as dolutegravir or bictegravir) given their high efficacy, good tolerability, and high barrier to resistance, often available as convenient single tablet, once daily fixed dose combinations that support adherence.
• Adherence is the single most important determinant of treatment success, since inconsistent adherence risks the development of resistance and subsequent treatment failure; adherence support, addressing practical, psychological, and social barriers, is a core and ongoing component of care rather than a one time counseling point.
• Opportunistic infection prophylaxis is indicated at specific CD4 thresholds: co-trimoxazole prophylaxis against Pneumocystis jirovecii pneumonia and toxoplasmosis is typically started when CD4 falls below approximately 200 cells per microliter, and can be discontinued once the CD4 count has recovered above this threshold on effective antiretroviral therapy for a sustained period.
• Immune reconstitution inflammatory syndrome is a recognized complication of starting antiretroviral therapy, particularly in patients with a very low CD4 count and an underlying, sometimes previously subclinical, opportunistic infection.
• Regular monitoring includes CD4 count and viral load at intervals guided by treatment stability (viral load should become undetectable within several months of starting effective therapy, and maintaining an undetectable viral load is both the marker of treatment success and, importantly, means the person cannot sexually transmit HIV, the basis of the "undetectable equals untransmittable" principle now central to modern HIV counseling).
• Pre-exposure prophylaxis (PrEP), using antiretroviral medication in HIV negative individuals at ongoing substantial risk of acquisition, and post-exposure prophylaxis (PEP), started as soon as possible (and within 72 hours) after a specific high risk exposure, are both important prevention tools, complementing treatment as prevention in reducing population level HIV transmission.
• Prevention of mother to child transmission combines maternal antiretroviral therapy throughout pregnancy (ideally with a fully suppressed viral load well before delivery), consideration of mode of delivery based on viral load near term, neonatal post exposure prophylaxis, and guidance on infant feeding, together reducing transmission risk to well under 1% in optimally managed settings.

Referral: HIV or infectious disease specialist service for all newly diagnosed patients, for treatment initiation and ongoing long term management; obstetric and specialist HIV input for all pregnant patients living with HIV, given the specific considerations around preventing vertical transmission.