An epidemiologic study that examined tuberculosis cases in urban settings in the United States from 2000 to 2007 contained good and bad news. The good news is that none of the cities surveyed had a significantly increasing incidence rate (the number of cases newly diagnosed per 100,000 population). The bad news is that 29 (60%) of the 48 cities studied showed no significant decline in incidence rates during the eight years. From among the 100 largest U.S. cities, the investigators selected those that had at least 20 annual cases of tuberculosis during the study period, as reported to the Centers for Disease Control and Prevention's National Tuberculosis Surveillance System. The cities studied ranged in population from 207,000 to 8,156,000. Changes in case count (prevalence) over the study period ranged from a decrease of 76% to an increase of 56%. The study found no correlation between the population size of the cities and tuberculosis incidence.

Figure. Kevin Lisboa in a detention ward at Bellevue Hospital in New York City in 2006. Tuberculosis patients in New York City who refuse treatment can still be sent to a dedicated hospital ward until no longer infectious. Photo by Fred R. Conrad /

Although the number of tuberculosis cases in the cities studied constituted 36% of all reported cases in the United States, those cities' populations represent only 15% of the U.S. population. The authors point out that the world's population is rapidly becoming more concentrated in urban areas and the marginalized groups known to be at higher risk for tuberculosis are becoming concentrated in those areas; in light of these trends, they maintain, the study's findings contain more reason for concern than comfort.

One percent of the patients had multidrug resistance, which was observed more frequently in cities with declining tuberculosis rates. Oddly, those cities were also associated with an almost 20% lower reported use of directly observed therapy (DOT), which is known to reduce the frequency of acquired drug resistance. The authors suggested several explanations for the different rates of reported DOT use, including possible record-keeping errors in the source data and the direction of resources in those cities to other control strategies.

Noting that the study's design made it impossible to determine which patient factors were associated with a lower incidence of tuberculosis, the authors urged that further studies be undertaken to determine what specific features of urban settings shape health so that current interventions can be enhanced and new areas of focus can be identified. -David Carter

REFERENCE