Prescription reporting strengthens surveillance
A two-drug search turns up 18% more cases
Even though TB case reporting is universally mandatory, hardly anyone claims it’s foolproof. The fact that state laboratories also are required by law to report positive TB cultures offers one good backup for the system, TB experts agree.
The problem with mandatory lab reporting is that it, too, has a hole through which cases can slip. That happens when the diagnosis of TB is made presumptively, based only on clinical symptoms in the absence of a positive culture.
That’s why requiring pharmacies to report patients whose doctors prescribe two anti-TB drugs might be a third useful adjunct to surveillance efforts, explains Deborah Yokoe, MD, MPH, associate epidemiologist at Brigham and Women’s Hospital in Boston and lead author of a recent study in which data from a health maintenance organization were used to supplement surveillance.1
By checking pharmacy records of a big Massachusetts-based HMO, Yokoe found that 18% of cases ferreted out by a search of the HMO’s pharmacy records were not known to the state health department. The cases probably weren’t reported, she adds, because of physicians’ heavy workloads and the absence of positive cultures in all instances in which cases went unreported.
"Reporting [TB cases] isn’t something doctors are necessarily good at, especially if it takes a lot of time or if they have a lot of cases," says Yokoe. "Sometimes they’re simply more focused on patient care than paperwork; other times they’re not sure whether a patient fits the case definition."
The 18% gap, though it may strike some as big, may not be atypical, Yokoe adds. In two other studies, one in Italy and the other in Puerto Rico, researchers found a slightly larger proportion of unreported cases.
Some TB control divisions already mandate pharmacy reporting. Tacoma/Pierce County, WA, for example, just inaugurated the practice. (See cover story.) Mandatory pharmacy reporting for anti-TB drugs has been in place for many years in Baltimore. There, TB control officer Darryl Harge says he doesn’t think the practice has ever turned up an extra case because virtually all cases in the city are managed by TB control.
Yokoe and colleagues found that searching for two or more anti-TB drugs yields the best results: a sensitivity of 89% and a positive predictive value of 30%. What keeps specificity low is that anti-TB drugs also can be prescribed for other mycobacterial infections or for unrelated conditions.
Reference
1. Yokoe DS, Subramanyan GS, Nardell E, et al. Supplementing TB surveillance with automated data from health maintenance organizations. Emerg Infect Dis 1999; 5:779-787.
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