The major public health screening efforts in the United States have been for tuberculosis and sexually transmitted infections (syphilis, chlamydia, gonorrhea, HIV, and herpes simplex virus). Hepatitis screening is used primarily for blood donation, institutionalized populations, and health care workers rather than for the general population. These disorders are discussed in more detail in Chapter 14.
One-third of the world’s population is infected with Mycobacterium tuberculosis (TB). The prevalence of TB has recently increased in the United States, reversing decades of steady decline. Thus, TB skin testing should be performed on individuals in high-risk groups, and positive results should prompt chest radiography and consideration of chemoprophylaxis. Some experts advocate regular skin testing of all persons younger than 35 years at the time of routine health examination (for detection as well as for baseline data). The US Occupational Safety and Health Administration recommends that all health care facilities conduct a TB risk assessment, with testing performed if indicated; routine testing is no longer recommended. In addition to TB skin testing, an interferon-gamma release assay (IGRA) can be used to screen for TB exposure. This blood test may be more specific in some clinical situations, including screening for TB in patients who previously received the BCG vaccine. Although acid-fast smears and histopathology remain the most common approach for confirming a diagnosis of TB, a number of nucleic acid amplification assays are also now available.
Several candidate vaccines for TB are currently being investigated; they include subunit; recombinant BCG; and inactivated whole-cell vaccines. The current BCG vaccine can also provide limited protection to newborns in endemic areas.
The incidence of syphilis is increasing in the United States, particularly among men who have sexual intercourse with other men. Syphilis is almost always transmitted sexually; congenital disease transmitted in utero still occurs but is rare (600 cases in the United States in 2016). The incidence of congenital syphilis has dropped 90% since the 1940s because of required premarital screening and pregnancy screening. Better prenatal care and increased syphilis screening during pregnancy improve the likelihood of detecting infants at risk for congenital syphilis, thus allowing early maternal treatment.
Latent, untreated cases of syphilis in which the primary or secondary mucocutaneous lesion is no longer present can be detected only by screening. It is important to detect early latent disease: in approximately 25% of cases, infectious mucocutaneous lesions reemerge spontaneously in the first 2 years. Late latent disease should be detected and treated because of the long-term destructive effects on the central nervous system, the aorta, and the skeletal system.
Screening is generally performed with the more sensitive, but less specific, nontreponemal antigen tests (VDRL, RPR, TRUST). Positive results are then confirmed with treponemal antigen tests (FTA-ABS, MHA-TP, TPPA, TP-EIA), which were more expensive in the past; automation of these treponemal antigen tests has decreased their costs, and these tests are now sometimes used for the initial screening.
Bibbins-Domingo K, Grossman DC, Curry SJ, et al; US Preventive Services Task Force (USPSTF). Screening for syphilis infection in nonpregnant adults and adolescents: US Preventive Services Task Force recommendation statement. JAMA. 2016;315(21): 2321–2327.
Excerpted from BCSC 2020-2021 series: Section 1 - Update on General Medicine. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.