Direct nucleic acid amplification testing improves TB diagnosis
Though we still do not have a point of care diagnostic that is cheap, fast, and detects all TB including in people with HIV and children, there has been some improvement in diagnosis with direct nucleic acid amplification testing as the following article shows.
NEW YORK Jun 06 - Mycobacterium tuberculosis direct nucleic acid amplification testing improves diagnostic accuracy and timeliness and reduces unnecessary treatment, according to a retrospective cohort analysis.
"CDC recommends nucleic acid amplification testing (NAAT) on at least one (preferably the first) respiratory specimen for all patients suspected of having pulmonary TB," Dr. Suzanne M. Marks from the U.S. Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, told Reuters Health by email.
"The Mycobacterium tuberculosis Direct (MTD) NAAT is more accurate and timely in diagnosing TB disease than standard diagnostics using the AFB (acid-fast bacilli) smear," she said.
While AFB smear is cheap and simple, it has poor sensitivity, especially in patients infected with HIV. The gold standard culture takes two to eight weeks for results, whereas NAAT for M. tuberculosis can yield results within 24-48 hours.
Dr. Marks and colleagues evaluated the use, effectiveness, health-system benefits, and cost-effectiveness of MTD in an analysis of 2,140 patients with suspected pulmonary tuberculosis.
Forty percent of patients had at least one smear-positive specimen, and 60% had all smear-negative specimens, according to the report, published online May 22 in Clinical Infectious Diseases. More than one-third (37%) of the cultures were positive.
Overall, 59% of hospitalized patients received MTD, compared with 25% of those not hospitalized. The turn-around time from specimen collection to reported MTD result averaged 2.6 days for hospital specimens and 4.0 days for clinic specimens.
In all subpopulations examined (HIV-infected, homeless, substance abuser, foreign-born), MTD showed higher positive predictive value, sensitivity, and negative predictive value than no-MTD.
In all subpopulations except those with homelessness, MTD also proved more specific than no-MTD.
Average days on outpatient medications was 53 days fewer for MTD-negative patients having smear-positive/culture-negative specimens and 42 days fewer for smear-negative/culture-negative patients, compared with similar no-MTD patients.
In multivariable analysis, MTD-positive results significantly shortened the time to TB determination, but MTD did not significantly decrease the time to TB exclusion for culture-negative patients.
Health-system costs were higher overall for patients who received MTD than for patients with no-MTD. However, in patients with HIV or homelessness, MTD brought substantial incremental cost savings to diagnose or to exclude TB, and in patients with substance abuse, MTD cut the cost of excluding TB in those with smear-negative specimens.
"We found (...) significant health-system benefits in improving diagnostic accuracy, reduced time to TB diagnosis in smear-positive/MTD(+), reductions in medical procedures and respiratory isolation for patients having smear-positive/MTD(-)/culture-negative specimens, less time (average 1.5 months) taking unnecessary TB medications, and fewer resources expended on contact investigation for patients whose specimens were smear-positive/MTD(-)/culture-negative compared with no MTD," the researchers write."If sites are not currently using MTD NAAT, our study suggests that there are savings if MTD NAAT is used in patients with HIV-infection, homelessness, and substance abuse," Dr. Marks concluded. "In some other populations, MTD NAAT might be considered cost-effective versus not using it."
She added, "Per capita gross domestic product (GDP) is often used as a standard to compare whether an intervention is cost-effective. In 2010, the U.S. per capita GDP was $46,612. Compared to that, the MTD NAAT was cost-effective in all sub-populations examined except two."
"The 2013 updated 'Guidelines for Prevention and Treatment of Opportunistic Infections in HIV-Infected Adults and Adolescents' (http://aidsinfo.nih.gov/guidelines) also recommend NAAT for patients with advanced immunodeficiency who are at risk of rapid clinical progression of TB because of their high positive predictive value in smear-positives and sensitivity in smear-negatives," Dr. Marks said. "Patients with HIV infection are at high risk of dying from TB and transmitting TB infection among HIV-infected contacts if not diagnosed early."
SOURCE: http://bit.ly/11jdvrC
Clin Infect Dis 2013.
Source: Medscape Today
