The Third Epidemic—Multidrug-Resistant Tuberculosis: Discussion
During the past decade, the incidences of HIV infection and ТВ have ascended to epidemic proportions in several major US cities. At Bellevue Hospital Center in Manhattan, the incidence of MDR-TB has increased sevenfold in 1991 as compared with any of the previous 20 years. buy antibiotics online
Several case series have been reported by the Centers for Disease Control in which M tuberculosis isolates were resistant to first-line anti-ТВ medications. In a cooperative Centers for Disease Control-New York City Department of Health study, 466 cultures positive for M tuberculosis were tested for drug susceptibilities from laboratories throughout the city collected during April 1991. Thirty-three percent had resistance to one or more anti-ТВ drugs and almost 20 percent had resistance to both isoniazid plus rifampin. Patients who were currently or previously treated with anti-ТВ drugs were more likely to have resistant organisms than those who had not been previously treated. Of isolates obtained from Bellevue for this cooperative study, 13 of 50 (26 percent) were resistant to both isoniazid plus rifampin, suggesting that our reported rates may actually be underestimates. Chawla and colleagues found an overall resistance rate of 30.9 percent to one or more drugs at Kings County Hospital in Brooklyn. More than half (56.6 percent) of those resistant were resistant to more than one drug. They found a combined pattern of isoniazid-plus-rifampin resistance in 30.2 percent of cases. Our results showed an overall resistance rate of 33 percent, and also that patients were most commonly resistant to isoniazid (25 percent) followed by rifampin (20 percent). Our patient population showed a similar distribution with an isoniazid-rifampin resistance of 16 percent and an isoniazid-rifampin-streptomycin-ethambutol resistance of 13 percent. These figures are especially disturbing, since the case fatality rate for MDR-TB exceeds 50 percent, and approaches 90 percent among HIV-positive individuals.
Although ТВ is a well-known problem among the homeless, their overall incidence of active ТВ and prevalence of ТВ infection are unknown. Clinics and shelters have shown active disease ranging from 1.6 to 6.8 percent and ТВ infection from 18 to 51 percent. Shelters offer substantial potential for transmission of ТВ, especially during the winter months when there is overcrowding and poor ventilation. Screening and preventive therapy programs among the homeless have been largely ineffective due to poor patient compliance to treatment regimens and follow-up visits.
The epidemic of MDR-TB can be attributed to both noncompliance with therapy and nosocomial spread. Individuals who are homeless, jobless, and addicted to intravenous drugs, alcohol, and tobacco place a low priority on taking multiple pills on a daily basis. After a hospitalization for several weeks, their symptoms are diminished and they frequently leave without permission, or if discharged, fail to take their medication or return for clinic follow-up visits. Other factors that increase the chances of infection by MDR-TB are birth and/or recent residence in an endemic area and recent exposure to a drug-resistant strain or infection with other mycobacteria. Nosocomial spread of MDR-TB has been reported in a hostel for AIDS patients and in hospital wards where a high percentage of HIV-positive patients are hospitalized (eg, virology or medicine services). In studies performed by the Centers for Disease Control, most of the exposed persons who developed active MDR-TB were known to be HIV-positive.
Our results also demonstrate the close correlation between intravenous drug use and active ТВ, although intravenous drug use is not an independent risk factor for drug resistance. Intravenous drug dependency poses a high risk for both the development of disease from infection and the acquisition of new infection. Importantly, Selwyn and colleagues showed that although the incidence of ТВ infection was similar for both HIV-positive and HIV-negative intravenous drug abusers, the risk of active ТВ was elevated only for seropositive subjects. The magnitude of the current ТВ problem is best stated by Bloom and Murray, “… If we do not learn from the current epidemic of ТВ and if we do not develop new scientific tools to diagnose, prevent, and treat the disease, the tragedy unfolding in New York City could be repeated in any city in America that has homeless people, AIDS, prisons, hospitals, and nursing homes.”