In an area of high tuberculosis (TB) incidence, investigators found that the age-adjusted rate of disease reinfection after successful treatment for TB was four times that for new cases, according to a study in the American Thoracic Society's (ATS) peer-reviewed journal. The objective of the researchers' study was to determine the incidence rate of TB attributable to reinfection among those successfully treated for the disease at an epidemiologic fieldsite in Cape Town, South Africa. The median follow-up period was slightly over five years.
In the study, all patients with reported TB in the area between years 1993 to 1998 were followed-up to 2001 for disease either needing retreatment or having recurred. Patients were excluded who were either multi-drug-resistant or who had treatment failure, were transferred, or died during treatment. The researchers restricted analysis to patients for whom DNA fingerprinting of their TB isolates had been obtained.
The incidence of new bacteriologically confirmed TB in the Cape Town area was 313 cases per 100,000 population. In the United States, the rate was 5.1 cases per 100,000 in 2003.
Recurrent TB occurred in 108 (18 percent) of 612 patients for whom the researchers had DNA fingerprints of TB isolates. Of this group, 61 (14 percent) of 447 experienced recurrence after successful treatment, and 47 (28 percent) of the remaining 165 had recurrent disease after they had defaulted on their treatment.
According to the authors, the rate of disease reinfection was approximately seven times the crude incidence rate and approximately four times the age-adjusted incidence rate of new TB in the area.
The study appears in the second issue for June 2005 of the ATS's peer-reviewed American Journal of Respiratory and Critical Care Medicine.
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