Approach

Once a person has been diagnosed with HIV infection, it is important to measure their CD4 count, in addition to viral load. The CD4 count is a highly sensitive and specific marker that determines the susceptibility to particular opportunistic infections.[77]

  • Tuberculosis (TB) can occur at any CD4 count, but the risk increases with lower CD4 counts.​[1][47][78]​​​​

  • Individuals with a CD4 count less than 250 cells/microlitre living in or visiting areas in which Coccidioides species are endemic are at increased risk for coccidioidomycosis.[42]

  • The risk of Pneumocystis jirovecii pneumonia (PCP) and oropharyngeal or oesophageal candidiasis is significantly higher when the CD4 count is below 200 cells/microlitre.[1]

  • Individuals with a CD4 count below 150 cells/microlitre who live in or have travelled to areas endemic for Histoplasma capsulatum are at increased risk for developing progressive disseminated histoplasmosis.[1]

  • When the CD4 count is below 100 cells/microlitre, people are at a higher risk for toxoplasmosis.[1]

  • The risk of cytomegalovirus (CMV) end-organ disease and Mycobacterium avium complex (MAC) is highest when the CD4 count is below 50 cells/microlitre.[1]​ More than three-quarters of cryptococcal infections associated with AIDS develop when the CD4 count falls below 50 cells/microlitre.[54]

Individuals who are not receiving suppressive antiretroviral treatment are more likely to develop opportunistic infections.[57]

Tuberculosis

The diagnosis of TB in people living with HIV can be can be challenging, as it may present with signs and symptoms (such as fevers, weight loss, and malaise) that may be attributed to HIV itself, and the clinical manifestations of pulmonary TB may be different depending on the level of immunosuppression.[2] Individuals with a CD4 count less than 350 cells/microlitre are more likely to present with less common manifestations of TB, such as lower lobe pulmonary disease, miliary disease, and extrapulmonary disease.[79] Whether or not a person has pulmonary signs or symptoms, evaluations for TB should begin with a chest x-ray, or even a computed tomography (CT) scan if feasible, since CT scans may detect infiltrates not seen on a chest x-ray.[80] Depending on the involved site, TB may present with shortness of breath, cough, lymphadenopathy, headache, meningism, abdominal pain, dysuria, or abscess formation.

A high index of suspicion must be maintained when evaluating people living with HIV with symptoms suggestive of TB, as chest x-rays may appear normal.[81] Diagnostic work-ups should include smear, culture, and nucleic acid testing if available, and should be targeted based on the anatomical site of involvement (e.g., respiratory specimen or other tissue or fluid sample).[1]

Acid-fast bacilli (AFB) stain and culture

  • Three sputum specimens should be obtained for AFB smear, and culture.[82]

  • Specimens obtained through bronchoscopy with bronchoalveolar lavage and trans-bronchial biopsy may be useful in the evaluation of a person with an abnormal chest x-ray when sputum smears are negative.

  • In extrapulmonary TB, AFB smear and cultures should also be performed on specimens from other sites.[82]​​

Molecular tests (nucleic acid amplification; polymerase chain reaction [PCR])

  • Several rapid nucleic acid amplification tests (NAATs) are available for the diagnosis of TB, and some are also able to detect resistance to some TB drugs.[83][84][85][86][87][88]​​​​​​​​​​​ Since NAATs are more sensitive than smears, and can help distinguish between M tuberculosis and non-tuberculous mycobacteria, they should be performed on at least one specimen from individuals with suspected pulmonary TB.[89]​ Although NAATs were originally designed and approved for respiratory specimens, they may also be requested on specimens from other sites where involvement of TB is suspected (e.g., cerebrospinal fluid, lymph node aspirate, lymph node biopsy, pleural fluid, peritoneal fluid, pericardial fluid, synovial fluid, or urine).[83] In the US, use of NAATs for extrapulmonary specimens is not approved by the US Food and Drug Administration and therefore use in this setting is off-label.

Lipoarabinomannan assay

  • Lateral flow tests that detect lipoarabinomannan (LAM) antigen in urine have emerged as potential adjunctive point-of-care tests in certain countries. One Cochrane review found the lateral flow urine lipoarabinomannan (LF-LAM) assay to have a sensitivity of 42% and specificity of 91% in diagnosing TB in HIV-positive individuals with TB symptoms.[90]

  • The World Health Organization (WHO) recommends that LF-LAM can be used to assist in the diagnosis of active TB in HIV-positive individuals, when used in combination with other tests.[83] This approach is supported by another Cochrane review, which found reductions in mortality and an increase in treatment initiation with use of LF-LAM in inpatient and outpatient settings.[91]​ Culture would still be required for drug susceptibility testing.

In vitro assays

  • High levels of adenosine deaminase (ADA) in pleural fluid have been shown to be highly sensitive and specific for TB pleuritis, regardless of CD4 count. Although other conditions, such as cancer, may also cause elevated pleural fluid ADA, the levels generally do not exceed the cut-off values suggested for TB.[92] In one study, adenosine deaminase sensitivity was 94% and specificity 95% in people living with HIV, regardless of CD4 counts, when the cut-off value was 30 U/L.[93]

Imaging

  • Chest x-ray should be performed on all individuals with suspected TB. An upper lobe infiltrate, with or without cavities, is highly suggestive of pulmonary TB, although many people with HIV and TB coinfection present with atypical chest x-rays.[94] Individuals with a CD4 count less than 200 cells/microlitre can have TB culture-positive sputum and a normal chest x-ray.

  • Computed tomography (CT) scanning is useful for detecting pulmonary TB in individuals with normal chest x-rays and for detecting extrapulmonary lesions. CT of the head is recommended if TB meningitis is suspected; findings include tuberculomas, post-contrast basal enhancement, hydrocephalus, and infarcts.[95] CT of the abdomen should be considered in individuals with abdominal pain.

Biopsy

  • May be trans-bronchial or of an extrapulmonary site (e.g., bone marrow, vertebral column, liver, lymph node).

  • On pathological examination, tuberculous granulomas are detected in 60% to 100% of cases, depending on the individual's immune status and the site of sampling.[96]

  • The specimen obtained should also be examined for AFB and cultured for mycobacteria.

Blood cultures

  • Mycobacterial blood cultures may be positive in disseminated TB.[97]

Disseminated MAC disease

Disseminated MAC disease only occurs in people with advanced immunosuppression; in people living with HIV, it mainly occurs in those with a CD4 count less than 50 cells/microlitre. Clinical presentation may include non-specific symptoms and signs, such as high fever, night sweats, fatigue, weight loss, anaemia, and anorexia. Abdominal pain may result from involvement of retro-peritoneal lymph nodes and chronic diarrhoea from gut mucosal involvement. Other manifestations include hepatosplenomegaly, lymphadenopathy, and leukopenia. More unusual presentations include palatal and gingival ulceration, septic arthritis, osteomyelitis, endophthalmitis, pericarditis, and gastrointestinal (GI) bleeding.[98][99][100]

Laboratory investigations

  • Full blood count (FBC) may show anaemia (often severe, haematocrit <25%) and leukopenia.

  • Abnormal liver function tests, including elevated alkaline phosphatase and lactate dehydrogenase (LDH), and low albumin.

  • Cultures: AFB blood cultures detect over 90% of cases and are the test of choice for the diagnosis of disseminated MAC; they should be drawn from all individuals with risk factors and clinical features.[101][102]​​ MAC will not grow in standard blood culture media. Species identification can be established using DNA probes, and the isolation of MAC from other sterile sites, such as bone marrow, lymph nodes, joints, and gastrointestinal specimens may also be useful.[103]

Imaging

  • An abdominal CT can be helpful in the diagnostic evaluation of a person with disseminated MAC as it is likely to demonstrate mesenteric and abdominal lymph node enlargement, as well as hepatosplenomegaly and small bowel wall thickening.[104] However, normal abdominal CT scans have been reported in 25% of individuals with AIDS with disseminated MAC.[105]

P jirovecii pneumonia

Individuals with Pneumocystis pneumonia (PCP) typically present with worsening dyspnoea with exertion, fever, and non-productive cough. Compared with individuals who are medically immunosuppressed without HIV infection, those with HIV generally have symptoms that progress over a longer duration (28 days, on average, compared with 5 days, respectively).[106][107]

The initial evaluation of a person suspected of having PCP should begin with a chest x-ray. If the chest x-ray appears normal but PCP is suspected, a high-resolution CT (HRCT) should be ordered.[1]

The diagnosis of PCP is established by visualisation of the cystic or trophic forms in respiratory specimens obtained from induced sputum or bronchoscopy with bronchoalveolar lavage (BAL), which has a significantly higher diagnostic yield.[108]Pneumocystis cannot be cultured.

Laboratory investigations

  • Serum lactate dehydrogenase (LDH) concentration is frequently increased and may be suggestive of PCP in individuals with risk factors and compatible clinical features.[109]

  • Decreased blood oxygenation is the most common laboratory finding among individuals with PCP. Widened alveolar-arterial oxygen (PAO₂-PaO₂) gradients have been reported in >90% of cases, and the magnitude can reflect disease severity and be useful for monitoring in severe cases.[110] Oxygen desaturation during exertion can be an especially sensitive finding.[111]

  • Beta-D-glucan, a cell wall component of most fungi, may be useful for non-invasive diagnosis. Although raised beta-D-glucan is not specific to PCP, it should raise suspicion if raised in a person with risk factors and a compatible clinical presentation.[112]

Sputum induction (by inhalation of aerosolised hypertonic saline solution)

  • The diagnostic yield of expectorated sputum is too low to be of any clinical utility. Examination of induced sputum is recommended as the initial screening test. Since the negative predictive value of this test is relatively low, a negative test should prompt a referral for fibreoptic bronchoscopy with BAL, which significantly increases the diagnostic yield to >90%.[108] Specimens should be evaluated with particular staining methods (e.g., Gomori-methenamine silver, Wright-Giemsa, Diff-Quick, or immunofluorescence). PCR is increasingly used to aid in the diagnosis of PCP. While a positive test may reflect colonisation rather than active disease, a negative test from a lower respiratory tract specimen can be used to confidently exclude PCP.[1][112]

Imaging

  • Chest x-ray should be performed on all the individuals with suspected PCP. A diffuse interstitial infiltrate is typical. Cavitation or cystic lesions, abscess, lobar consolidation, nodular lesions, effusions, and pneumothorax are less common presentations.[113] Upper lobe infiltrates may be seen in individuals with PCP who are using aerosolised pentamidine.[114]

  • CT of the chest: HRCT has a sensitivity of 100%, and should be considered when the chest x-ray is normal, since a normal HRCT essentially rules out PCP. HRCT findings in people with early PCP include reticular, nodular, and ground glass opacities. In more advanced cases, CT can demonstrate consolidations, upper lobe thin-walled cysts, or pneumothoraces.[115]

Biopsy

  • Transbronchial biopsies can be performed if initial BAL is negative but clinical suspicion of PCP is high or other diagnoses are considered likely. Sensitivity of transbronchial biopsies is 95% to 100%.[1]

  • Open biopsy is no longer recommended, given the advantages of BAL and molecular techniques. In rare cases, video-assisted thoracic surgery biopsies are considered when bronchoscopy is inconclusive.

Toxoplasmosis

In people with AIDS, toxoplasmic encephalitis generally presents with fever and symptoms of encephalitis, including headache, seizures, motor weakness, and/or a range of mental status changes.[116] Less common extracerebral manifestations include pneumonitis and chorioretinitis.[117][118]​​ Gastrointestinal and musculoskeletal involvement may also occur.

A presumptive diagnosis can be made with a 90% probability in a person with CD4 count below 100 cells/microlitre and:

  • Seropositivity for Toxoplasma gondii immunoglobulin G (IgG) antibodies

  • Lack of effective previous prophylaxis for toxoplasma

  • Brain imaging with typical radiographical appearance (such as multiple ring-enhancing lesions).

In such cases, it is common practice to treat empirically for toxoplasmosis. However, if the person does not respond to empirical therapy after 2 weeks (based on clinical or radiographical improvement), a brain biopsy should be performed.[119]

Serology

  • Seropositivity for anti-toxoplasma IgG antibodies makes the diagnosis more likely; however, absence of these antibodies does not exclude it.

Lumbar puncture

  • Cerebrospinal fluid (CSF) findings are nonspecific and often show mild mononuclear pleocytosis and elevated protein. Giemsa staining can show tachyzoites. Detection of T gondii in the CSF by PCR establishes the diagnosis, yet a negative result does not rule it out.[120]

Imaging

  • CT and magnetic resonance imaging (MRI) should be considered; MRI is more sensitive than CT.[121] CT and MRI of the brain usually show ring-enhancing lesions, often associated with oedema. Multiple lesions are more common than single lesions.[122]

  • Thallium single photon emission CT (SPECT) and positron emission tomography (PET) can be useful in distinguishing toxoplasmosis (or other intra-cranial infections) from central nervous system lymphoma.[123][124]​​ To differentiate cerebral lymphoma from toxoplasma encephalitis, a F-fluorodeoxyglucose (FDG) PET scan may be helpful; F-FDG uptake is typically significantly higher in cerebral lymphoma. Thallium scans in the era of ART are of limited utility.[125][126]

Brain biopsy (open or stereotactic)

  • Establishes a definitive diagnosis of cerebral toxoplasmosis, although individuals are typically treated based on a presumptive diagnosis without a brain biopsy, which is associated with a significantly high risk of complications. PCR testing for toxoplasma also establishes a definitive diagnosis and has made brain biopsies less necessary.[127]

CMV

Retinitis is the most common clinical presentation of CMV disease in people with AIDS and can cause severe visual impairment. Fundoscopic examination is helpful. Visual floaters are common, and areas of infarction, haemorrhage, perivascular fluffy white retinal infiltrates, and retinal opacification are often seen.[128] The diagnosis is made clinically by an ophthalmologist. Other less common manifestations may include colitis (second most common), ventriculitis, cholangitis, encephalitis, and gastritis.[129] Pain and weakness may indicate the presence of CMV polyradiculopathy.​​[130]

Laboratory investigations

  • FBC may show anaemia, leukopenia, or thrombocytopenia.

  • Serology: CMV-related disease is based upon the clinical presentation and, when possible, the identification of virus in tissue. Routine CMV serology is not recommended for the purpose of confirming CMV disease in people with HIV, since a significant proportion of this population is seropositive.[131]​ However, CMV IgG may be considered if blood transfusion is contemplated in a person at low risk for CMV exposure. A negative CMV IgG may support use of CMV-free blood products.[131]​ Serology is not useful for diagnosing CMV retinitis.

  • Quantitative CMV PCR testing is of limited utility and not recommended for people living with HIV, since viraemia may be present in the absence of CMV disease. Additionally, the test's performance is constrained: at a cut-off of 400 copies/mL (the limit of detection for CMV viraemia), its sensitivity is only 47%, and the negative predictive value is 70%.[132] Moreover, CMV viraemia is absent in more than half of individuals with CMV retinitis.[133]

Cryptococcus infection

Usually presents as a sub-acute meningitis or meningoencephalitis with fever, malaise, and headache. Individuals can also present with neck stiffness, photophobia, vomiting, and altered mental status. Disseminated disease can also occur, with or without concurrent meningitis. In such cases, pulmonary involvement or skin lesions may be present.

Lumbar puncture

  • Lumbar puncture is required for the diagnosis. Opening pressure of the spinal fluid should be measured as it is elevated (with pressures >200 mm of H₂O) in up to 75% of individuals.

  • CSF findings are often fairly unremarkable, with minimally elevated mononuclear cells and protein and decreased or normal glucose; the CSF profile can be normal in approximately a quarter of cases.[134][135]​​​​ India ink examination of the CSF remains a rapid test that is positive in more than 60% of people with AIDS with cryptococcal meningitis.[136]​ A negative India ink stain examination does not rule out infection, however. CSF cryptococcal antigen (CrAg) tests are highly sensitive and specific and should always be included in the diagnostic evaluation.[137] CSF fungal cultures should also be performed.

  • Serum CrAg should also be performed, as the sensitivity compares to that of CSF CrAG, and since lumbar punctures may sometimes be delayed or not feasible.[138]

  • Cryptococcal PCR assays are included in some multiplex PCR tests, although the performance and clinical value of these tests requires further study.[139]

Blood cultures

  • Three-quarters of people with HIV-associated cryptococcosis have positive blood cultures for Cryptococcus neoformans, which can grow on most bacterial and fungal media.[140]

Mucocutaneous candidiasis

Oral Candida infections can cause thrush, a common OI in people with AIDS characterised by creamy white, curd-like patches on the tongue and oral mucous membranes that can be removable by scraping. Thrush can be asymptomatic or can cause a cottony sensation in the mouth and potentially altered taste and difficulty swallowing.[141] Individuals may also develop Candida esophagitis, which can present with painful swallowing, an obstruction sensation, and sometimes substernal chest pain.[142] Mucosal candidiasis involving the vaginal and rectal regions can also occur, causing oedema, pruritis, and thick, curd-like discharge.[143]

Candidiasis is clinically diagnosed, usually based on characteristic symptoms and appearance of lesions.

Laboratory investigations

  • Diagnostic confirmation of thrush can be made with a scraping for microscopic examination, using a 10% potassium hydroxid (KOH) smear or gram stain, which may show characteristic findings, including hyphae, pseudohyphae, and budding yeast.[144]

  • Cultures are usually not necessary unless the lesions fail to resolve on antifungal treatment.

Imaging

  • Upper GI endoscopy is helpful in the diagnosis of oesophageal candidiasis.[145][146]

  • Barium swallow is of limited utility as the radiographical appearance alone cannot determine the cause of the lesions.

Coccidioidomycosis

The symptoms of pulmonary coccidioidomycosis are often similar to typical respiratory illnesses and individuals often present with signs and symptoms suggestive of a viral respiratory infection or community-acquired pneumonia; therefore, a high index of suspicion is important in people with endemic exposures.[147] While the typical incubation period is 1-3 weeks, individuals who develop immune suppression from advanced HIV infection can develop symptomatic disease several years after exposure.[148] Establishing the diagnosis of coccidioidomycosis depends on either detecting anticoccidioidal antibodies from blood, CSF, or other body fluid, or recovering Coccidioides species or spherules from a clinical specimen. Immunocompromised people, such as those with advanced HIV infection, may not be able to produce an antibody response, in which case antigen and/or PCR testing may be necessary, in addition to cultures.[149]

Culture

  • Isolation of Coccidioides organisms from a person’s sputum or other clinical specimen definitively establishes the diagnosis of coccidioidomycosis and should not be considered to represent colonisation. Organisms grow well within 5-7 days of incubation on most mycological and bacteriological media. When growth is noted, appropriate biocontainment measures are imperative, as cultures are highly infectious and laboratory personnel are at risk of infection.[150]​ 

Serology

  • Serological tests are most frequently used to diagnose primary pulmonary coccidioidomycosis and are highly specific for infection.[151] If serological testing is negative in suspected infection, repeat serological testing is recommended since it can take several weeks to develop an adequate antibody response.

  • Coccidioides serology should be performed in individuals with compatible clinical presentations if they have resided in or visited endemic regions.

  • Enzyme immunoassay (EIA) is widely available and detects specific IgM and IgG antibodies against Coccidioides. Positive EIA results should be confirmed with immunodiffusion and complement fixation.[1]

Antigen testing

  • Coccidioidal antigen testing can be performed on serum, urine, and CSF.

PCR

  • Real-time PCR can be used for detection of Coccidioides although availability is generally limited.

Imaging

  • Imaging studies, such as chest x-ray or CT scan, are typically useful during the initial evaluation but radiographical findings are non-specific.

Histoplasmosis

Disseminated histoplasmosis in individuals with HIV often presents with systemic symptoms such as fever, weight loss, fatigue, respiratory symptoms, and hepatosplenomegaly. It is a significant opportunistic infection in endemic regions and commonly occurs when CD4 counts are below 150 cells/microlitre.[1]​ Common clinical features include cough, dyspnoea, and GI symptoms such as diarrhoea, abdominal pain, nausea, and vomiting.[1][152][153]​​ Central nervous system (CNS) involvement can manifest as septic meningitis, seizures, or altered mental status. In severe cases, individuals may develop septic shock, multi-organ failure, or pericardial complications requiring urgent intervention.[1][43]

Antigen testing

  • Antigen detection tests for Histoplasma capsulatum are the preferred diagnostic method for disseminated histoplasmosis. These assays demonstrate high sensitivity and specificity, particularly in disseminated cases. They allow for rapid diagnosis, reducing the time to treatment initiation.[1]

  • Antigen testing can use non-invasive samples, such as urine or serum. It may also be performed on cerebrospinal fluid (CSF) and bronchoalveolar lavage fluid in cases involving the CNS or lungs.[1]

Culture[1]

  • Culture is a definitive diagnostic method for H capsulatum, but requires several weeks for results due to the slow growth of the organism.​

  • Blood cultures may be particularly useful for diagnosing disseminated histoplasmosis, especially in severely immunosuppressed individuals.

Histopathology[27]

  • Fungal-specific stains, such as Gomori methenamine silver, are used to identify the characteristic yeast forms of H capsulatum.

  • Periodic acid-Schiff staining can also be used to visualise fungal elements in tissue samples.

  • Histopathology is particularly useful for rapid presumptive diagnosis in acute clinical scenarios.

Molecular methods

  • PCR-based molecular diagnostic methods demonstrate high sensitivity and specificity for detecting Histoplasma DNA. These methods can serve as adjunctive tests, particularly when conventional diagnostics yield inconclusive results.

  • Availability and standardisation of molecular assays remain limited in clinical practice.

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