Preventing and treating infectious complications associated with HIV infection plays a major role in the management of HIV-infected persons. Determining the risk of past and ongoing risks for acquiring infections is an important goal of the initial history and baseline laboratory evaluation.[,] Key aspects of the history include past and current sexual practices, history of sexually transmitted diseases, history of injection drug use, travel or prior residence in an area endemic for fungal diseases, history of (or exposure to a person with) tuberculosis, and animal contact. Baseline testing can provide specific laboratory evidence of prior infection and can guide prevention efforts. Patients without evidence of prior infection can receive counseling for specific means to prevent infection, and those with evidence of prior infection may be candidates for specific preventive treatments. A number of tests should be performed as routine baseline screening for past or present infections in persons living with HIV infection (Figure 1).
Screening for Bacterial Infections
Routine baseline screening for bacterial sexually transmitted diseases pathogens is a high priority in HIV-infection because these infections occur at a higher incidence in HIV-infected patients and active infection with a sexually transmitted pathogen can increase the risk of forward HIV transmission. After a decline in syphilis rates in the United States during 1990-2000, rates have increased again, particularly among men who have sex with men (Figure 2). All HIV-infected adults, especially men who have sex with men, those with a history of sexually-transmitted diseases, and patients who have unprotected intercourse, should be screened for syphilis, using either treponemal test (enzyme immunoassay or chemiluminescent assay) or a nontreponemal test (Venereal Disease Research Lab [VDRL] or Rapid Plasma Reagin [RPR]. In addition to syphilis screening, routine baseline screening for all HIV-infected adults should include screening for urogenital chlamydia and gonorrhea. The nucleic acid amplification test (NAAT) is the recommended screening test for urethral or rectal Neisseria gonorrhoeae and Chlamydia trachomatis, and oropharyngeal Neisseria gonorrhoeae infection.[,] Screening for oropharyngeal C. trachomatis is not recommended. When testing for urethral infection, testing of a urine sample (not urethral swab) with NAAT is the preferred approach.
Cats can transmit Bartonella henselae to humans. Although his organism can potentially cause serious disease in HIV-infected persons with advanced immunosuppression, routine serologic testing of cats or HIV-infected persons to detect past infection with Bartonella has unknown utility and is not recommended.
Mycobacterium tuberculosis and a number of non-tuberculous mycobacteria (especially M. avium complex) are important pathogens in HIV-infected patients. Routine screening for latent tuberculosis infection is recommended for all HIV-infected persons using either (a) tuberculin skin testing with purified protein derivative (PPD) of M. tuberculosis or (b) an interferon-gamma release assays (IGRAs). Serologic tests to detect prior infection with M. avium complex or other non-tuberculous mycobacteria are not available, and blood cultures for M. avium complex are used for diagnostic purposes in symptomatic patients with advanced HIV disease, but not for routine screening.
Screening for Viral Infections
All HIV-infected individuals should undergo screening for prior infection with hepatitis A virus (HAV), hepatitis B virus (HBV), and hepatitis C virus (HCV). Among HIV-infected persons, evidence of HCV infection varies significantly depending on the risk factor for acquiring HIV (Figure 3), with infection rates of 60 to 90% among injection drug users, 4 to 10% among men who have sex with men, and 5 to 14% of those who acquired HIV heterosexually.[,] Those patients with chronic HBV or HCV infection who are co-infected with HIV have a greater risk of progression to chronic liver disease and may have a more rapid progression of HIV disease.[,] The HCV enzyme immunoassay is recommended as the initial screening test for HCV infection and those persons with a positive test should undergo confirmatory testing with a test to detect the presence of HCV RNA.[,] Screening for HBV should include antibody testing (anti-HBs and anti-HBc) plus antigen testing (HBsAg).
Evidence of prior infection with cytomegalovirus (CMV) has been found in greater than 90% of HIV-infected men who have sex with men and in greater than 70% of HIV-infected injection-drug users. According to the guidelines for the prevention and treatment of opportunistic infections, HIV-infected persons should undergo CMV antibody testing (anti-CMV IgG) only if they have a relatively low risk for CMV, namely those who have not had male-to-male sex contact and those who have not used injection drugs. Persons in high-risk groups for acquiring CMV disease are generally assumed seropositive for CMV. Routine screening for CMV infection using non-serologic laboratory markers, such as CMV antigen or quantitative CMV PCR, is not recommended. Those HIV-infected persons who are CMV seronegative can receive counseling on how to prevent exposure to CMV and, if they require a blood transfusion, they should receive CMV-negative blood products.
Routine serologic testing for herpes simplex virus (HSV) types 1 and 2 historically has not been recommended. More recently, however, some experts have recommend performing HSV serologic testing in HIV-infected persons to help identify unrecognized or asymptomatic HSV-2 infection. Serologic testing for varicella zoster virus (VZV) with anti-varicella IgG is should be considered for patients who do not recall having had chicken pox, in order to determine in advance the need for postexposure prophylaxis in the event of a VZV exposure. Human herpesvirus-8 (HHV-8), the agent responsible for Kaposi's sarcoma, Castleman's disease, and primary effusion lymphoma, occurs most frequently among men who have sex with men and transmission presumably occurs through contact with saliva, blood, and semen. Clinical use of routine serologic testing has not been established.
Screening for Parasitic Infections
Approximately 20 to 30% of HIV-infected adults in the United States have serologic evidence of prior infection with Toxoplasma gondii. In contrast, Toxoplasma infection occurs in up to 80% of the general population in France and among persons in certain regions of Africa. Because Toxoplasma encephalitis nearly always represents reactivation disease in HIV-infected patients, knowledge of Toxoplasma serostatus can prove extremely useful when evaluating an HIV-infected person with a brain mass lesion, though it does not establish or exclude the diagnosis. In addition, Toxoplasma serostatus can identify persons who should receive prophylaxis for Toxoplasma encephalitis. Patients without prior exposure to Toxoplasma should receive counseling on ways to reduce the risk of Toxoplasma infection, most importantly by avoiding contact with cat feces and by not eating undercooked red meat. Although other parasitic infections, such as cryptosporidiosis, isosporiasis, and microsporidiosis, can cause significant disease in HIV-infected persons, routine serologic tests for these pathogens are not recommended.
Screening for Fungal Infections
Skin testing with histoplasmin and serologic testing for prior infection with Histoplasma capsulatum do not predict subsequent development of histoplasmosis in HIV-infected persons, and thus these tests are not recommended. Histoplasma antigen tests are useful for the diagnosis of histoplasmosis in patients presenting with a compatible clinical syndrome, but have no role in routine screening. Similarly, skin testing with coccidioidin and serologic testing for prior infection with Coccidioides immitis are not recommended. Although routine serologic or antigen testing of all HIV-infected persons for infection with Cryptococcus neoformans is not recommended, some experts now recommend testing for serum cryptococcal antigen in patients with a CD4 count of 100 cells/mm3 or less; if the serum cryptococcal antigen test is positive, the patient should undergo evaluation for cryptococcal meninigitis. Serologic testing or antigen testing for prior infection with Candida species is not recommended. Exposure to Candida is universal and cannot be prevented.