TB decline not shared by foreign-born, urban areas
Overcrowding, socioeconomic status cited
Tuberculosis rates in the United States dropped 7% last year, but the disease remains entrenched in major urban areas, where overcrowded conditions and large foreign-born populations present unique challenges.
Tuberculosis morbidity findings from the Centers for Disease Control and Prevention (CDC) showed that new cases of TB dropped from 21,337 in 1996 to 19,855 in 1997.1 While the number of cases decreased in the six states that make up more than half of all TB cases (California, Florida, Illinois, New Jersey, New York, and Texas), nearly 40% of TB cases were reported in 64 major cities. (For the rates of change, see chart, p. 65.)
Reflecting the racial makeup of many urban cities, the CDC figures for 1997 found TB rates for Hispanics, African Americans, and Asian/Pacific Islanders were six, eight, and 16 times higher, respectively, than for whites. Although the cause for this disproportionate burden has been attributed to socioeconomic status, a new study published by the American Lung Association indicates that overcrowded living conditions play a major factor in transmission.
The study, published in the April Journal of Respiratory and Critical Care Medicine, found that socioeconomic status accounted for nearly half of the increased risk of TB previously attributed to race/ethnicity among U.S. minorities. Researchers conclude that people in lower income groups are more likely to live in crowded conditions, and the greater degree of crowding, the greater exposure to the TB germ.
"As long as we have crowded conditions, the probability is high that a person with TB will infect others before identification is made and treatment begins," says Matthew McKenna, MD, co-author of the study and an epidemiologist for the CDC. He adds that homelessness and erosion of public housing contributed to the recent TB epidemic.
Other factors: Foreign-born, HIV, MDR-TB
The proportion of TB cases found in foreign-born people has risen markedly, from 27% in 1992 to 39% in 1997, the CDC reports. With rates in this population four to five times higher than those for U.S.-born people, the CDC is taking steps to target prevention efforts to certain foreign-born groups and will develop recommendations possibly by this year. (See related story, at right.)
Although multidrug resistance also is attributed to the recent epidemic, nearly half (47%) of all MDR-TB cases were reported from New York and California last year. While 7.6% of isolates were resistant to isoniazid last year, only 1.3% were resistant to isoniazid and rifampin, marking a steady decline in recent years, the CDC reports.
The CDC received HIV status information for only half of the TB case reports for patients aged 25 to 44, and only 15 states reported HIV test results for at least three quarters of cases for that age group. In some locations, rates of TB cases in 25- to 44-year-olds co-infected with HIV reaches as high as 48%, underscoring the need for early diagnosis and therapy in this population. (See related story on new CDC guidelines for treating co-infection, p. 67.)
Reference
1. Centers for Disease Control and Prevention. Tuberculosis morbidity - United States, 1997. MMWR; 47:253-257.
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