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Rectal and Pharyngeal Screening Yields
Higher GC/CT Positive Rates in HIV+ Men
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IDSA/IDWeek 2015, October 7-11, San Diego
Mark Mascolini
Only 3% of all screening tests for gonorrhea (GC) and chlamydia (CT) yielded positive results in a large study of HIV-positive men [1]. But 12% of rectal CT screens and 6% of pharyngeal or rectal GC screens proved positive, findings that suggest a higher diagnostic yield when screening extragenital sites rather than just urine.
US guidelines call for annual urine screening for GC and CT in HIV-positive men who have sex with men (MSM), noted University of Colorado researchers and colleagues who conducted this study. Those guidelines recommend annual rectal screening for these sexually transmitted infections in men who have receptive anal intercourse and annual pharyngeal screening for GC.
The study involved all nucleic acid amplification tests (NAATs) for GC or CT in HIV-positive men from May 2012 through April 2015 in a Denver database. All men were in care at HIV clinics. Researchers excluded men seen at STI clinics or outreach centers because of incomplete data.
The investigators divided tests into screening tests and diagnostic tests. Screening tests were those for which (1) the provider designated the test as screening, (2) a history of present illness or review of symptoms did not document CDC-specified GC or CT symptoms, or (3) patients recently exposed to GC/CT were asymptomatic even if receiving prophylaxis during that visit. Diagnostic tests were those for which (1) the provider noted GC or CT symptoms before testing, (2) the history of present illness or review of symptoms did document CDC-specified GC or CT symptoms, or (3) symptoms were classified as genitourinary, rectal, pharyngeal, or other.
The Denver team reviewed 5755 tests done for 1232 men during the 3-year period. Median age measured 44 years (interquartile range 35 to 52). The researchers classified 81% of tests as screening and 19% as diagnostic. Among all tests, 65% assessed urine, 26% rectal samples, and 9% pharyngeal samples. Overall, 5% of all tests were positive for GC or CT. A higher proportion of diagnostic tests (10%) than screening tests (3%) came back positive, a highly significant difference (P < 0.001). Among all tests, a higher proportion of rectal tests proved positive (10%) than did pharyngeal tests (5%) or urine tests (3%) (P < 0.001).
The combined GC/CT positivity rate with diagnostic tests was highest for rectal tests (16%), followed by urine tests (10%) and pharyngeal tests (7%). Combined GC/CT positivity rates for screening tests were 9% with rectal tests, 4% with pharyngeal tests, and 1% with urine tests. For CT alone the highest positivity rate on diagnostic testing came with rectal tests (17%), trailed by urine tests (7%) and pharyngeal tests (7%). With screening tests, rectal, urine, and pharyngeal CT positivity rates were 12%, 2%, and 1%. For GC alone the highest positivity rate on diagnostic testing came on rectal tests (14%), followed by urine tests (13%) and pharyngeal tests (6%). With screening tests GC positivity was the same on rectal and pharyngeal tests (6%) but only 1% with urine tests.
Next the researchers determined the percentage of positive tests by symptom location. With genitourinary symptoms, positivity rates were highest for rectal tests (18%), followed by urine tests (11%) and pharyngeal tests (10%). For pharyngeal symptoms, rectal tests still had the highest positivity rate (8%), followed by pharyngeal tests (5%) and urine tests (4%). Finally, for rectal symptoms, rectal tests had the highest positivity rate (14%), followed by pharyngeal tests (5%). No urine tests came back positive with rectal symptoms.
The Denver team stressed that, even though only 3% of all screening tests yielded a positive result, 12% of rectal CT screening tests and 6% of pharyngeal or rectal GC screening tests proved positive. Those results, the researchers proposed, suggest that "screening extragenital sites may identify more infections than screening urine."
The investigators observed that symptom location often differed from anatomic site of infection, a result "suggesting a need to consider testing multiple sites regardless of reported symptoms, possibly depending on sexual practice."
Reference
1. Short R, Gardner E, Blum J, Vaughn S, Rowan S. Prevalence of gonorrhea and chlamydia infections among HIV-infected men by anatomic site and presence or absence of symptoms. IDWeek 2015, October 7-11, San Diego. Abstract 119.
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