Summary. After a decades-long decrease from 1953 through 1984 in the number of TB cases reported annually in the United States, TB has reemerged as a serious national problem. From 1985 through 1993, the number of new TB cases increased by 14%--from 22,201 to 25,313. During this period, approximately 64,000 more cases were reported than would have been predicted from the trend of decline from 1980 through 1984. The major factors contributing to this recent increase are (1) the association of TB with the HIV epidemic; (2) immigration from countries where TB is common; (3) the transmission of TB in congregate settings (e.g., health care facilities, correctional facilities, homeless shelters); and (4) a deterioration of the health care infrastructure. Some groups are at higher risk for TB than others. These groups can be divided into two categories: persons more likely to be exposed to or infected with M. tuberculosis and persons more likely to develop TB disease once infected.
In 1944, the year the U.S. Public Health Service Tuberculosis Program was created, more than 126,000 cases were reported. After the introduction of treatment for TB in the late 1940s, there was hope that TB would soon be eradicated. The number of reported cases declined by an average of 5.6% per year, from more than 84,000 cases in 1953 to 22,255 cases in 1984.
From 1985 through 1993, however, annual TB morbidity in the United States increased by 14%--from 22,201 to 25,313 cases. During this period, approximately 64,000 more cases of TB were reported than would have been predicted from the trend of decline from 1980 through 1984. These excess cases can be attributed to at least four factors: the HIV epidemic, immigration from countries where TB is common, the transmission of TB in congregate settings (e.g., health care facilities, correctional facilities, and homeless shelters), and a deterioration of the health care infrastructure.
An estimated 10 to 15 million persons in this country are infected with M. tuberculosis. TB disease may develop in these persons at some time in the future. In fact, the majority of new cases in the United States arise from this population. However, as the transmission of TB continues, newly infected persons are added to this population and become at risk for TB disease.
The following persons are more likely to be exposed to or infected with M. tuberculosis:
Many foreign-born persons from areas where TB is common acquire TB infection in their country of origin. In 1993, 30% of all new TB cases reported in the United States occurred in foreign-born persons, many of whom were probably infected before arrival in the United States. This percentage represents an increase over the percentage in previous years.
More than two thirds of TB cases reported in the United States occur in racial and ethnic minorities. Compared with non-Hispanic whites, Asians are 10 times more likely to have TB; blacks 8 times more likely; and Hispanics, Native Americans, and Alaskan Natives 5 times more likely. TB disease in blacks and Hispanics occurs more frequently in young adults, whereas in non-Hispanic whites, TB occurs most often in the elderly. One reason for the increased rates in racial and ethnic minorities may be that a greater proportion of these persons have other risk factors for TB, such as birth in a country where TB is common, HIV infection, low socioeconomic status, and exposure in a congregate setting.
Persons who are at a particularly high risk of developing TB disease once infected include:
HIV infection is the strongest known risk factor for the development of TB disease in persons with TB infection; for persons coinfected with M. tuberculosis and HIV, the risk of TB disease may be more than 100 times greater than for persons with TB infection alone.
Recent increases in TB cases reported in geographic areas and demographic populations with large numbers of AIDS cases suggest a strong association between the HIV epidemic and the increased TB morbidity. In 1991, a median of 9.5% (range, 0% - 61%) of patients from selected TB clinics, primarily in large urban centers, were also infected with HIV. In addition, approximately 5% of all AIDS cases reported in the AIDS case registry from 1981 through 1990 were also reported as TB cases in the TB registry.
Recently, several outbreaks of multidrug-resistant TB have occurred in hospitals and correctional facilities. Most of the cases in these outbreaks were caused by strains of M. tuberculosis resistant to isoniazid and rifampin, the two best TB drugs. Moreover, most of the patients involved in these outbreaks were HIV-infected persons. The morality rates were high, and multidrug-resistant TB was transmitted to health care workers.
Some correctional facilities have a large problem with TB transmission. A CDC study conducted in 1984 and 1985 showed that there were four times as many TB cases in persons living in correctional facilities as there were in persons of the same age living outside correctional facilities. Several factors may contribute to this difference, including (1) a high rate of TB infection in the prison population; (2) an increasing number of inmates infected with HIV and therefore at higher risk of developing TB disease once infected; and (3) overcrowding and inadequate ventilation in many correctional facilities, factors that increase the risk of transmission.
Nursing home residents may also be at relatively high risk for TB. In a 29-state survey conducted in 1984 and 1985, the CDC found that the rate of TB disease was twice as high for elderly persons living in nursing homes as for elderly persons not living in nursing homes.
Transmission continues to occur in the community at large. TB case rates are increasing for children younger than 15 years of age, especially for children younger than 5 years of age. Young children with TB must have been infected relatively recently; thus, TB cases in children indicate the transmission of TB in the home or community. In 1993, 84% of childhood cases of TB occurred in children from high-risk racial and ethnic populations.