Tuberculosis
Tuberculosis, the leading cause of death in the early 20th century,
appeared to be steadily decreasing in incidence with the advent of streptomycin in
1946, isoniazid in 1952, and rifampin in 1970. However, in 1985, the incidence in
the United States began to climb significantly. Between then and 1990, reported
cases increased by 16%, with a 10% increase in 1990 alone. This increase was the
largest since national reporting began in 1953.[68]
Most cases were from reactivation of old infection in immigrants or in patients
whose immune system had been compromised, and many cases involved multidrug-resistant
strains of Mycobacterium tuberculosis. Epidemic
transmission between hospitalized patients and from patients to health care workers
also occurred.[69]
[70]
Common to most of these cases was a low index of suspicion for tuberculosis, which
was occasionally not confirmed before postmortem examination.[71]
In response, in 1990 the CDC issued new guidelines for preventing
the transmission of tuberculosis in hospitals, and in 1992, the CDC published recommendations
for managing multidrug-resistant tuberculosis.[72]
[73]
Since then, the number of new cases of tuberculosis
has steadily declined such that the number of cases now being reported is the lowest
since 1953, the first year of reporting in the United States.[74]
In 1994, the CDC replaced all previous guidelines with a comprehensive new program
for the prevention of multidrug-resistant tuberculosis in health care facilities.
[75]
The program places the responsibility for
managing
prevention of tuberculosis on individual health care facilities rather than requiring
identical standards for all hospitals. Paramount are identification and treatment
of patients with tuberculosis; development of engineering controls, including isolation
rooms, filters, and ventilation; use of personal protective equipment; and implementation
of educational programs for health care workers. Anesthesiologists should be aware
of the applicability of these guidelines to the specialty.[68]
In 1996, the overall incidence of tuberculosis in the United States
was 8 cases per 100,000 population. The incidence was highest in the District of
Columbia (26/100,000), followed by Hawaii (17/100,000) and California (14/100,000).
The rate was highest in foreign-born persons (31/100,000), most of whom were from
Asia and the Caribbean. The goal of the CDC is to decrease the rate to less than
1 per million by 2010. Close attention will be paid to these cohorts.[74]
Tuberculosis spreads by small (1- to 5-µm) airborne droplets
released when an infected person speaks, coughs, sneezes, or sings. Transmission
of the bacillus is more likely in small, poorly ventilated areas and during cough-producing
procedures, including bronchoscopy and laryngoscopy. The probability of transmission
is also directly related to the concentration of infectious droplets and the duration
of exposure. In healthy persons who have inhaled contaminated droplets, the resulting
systemic infection is usually limited by the immune system within 2 to 10 weeks.
In these individuals, the risk of active tuberculosis developing after infection
is about 10%. The likelihood is higher in patients with HIV.[75]
All health care workers who are at high risk for exposure to M.
tuberculosis should be skin-tested at the time of employment. Those whose
test results are negative should be retested annually. The appearance of a positive
tuberculin skin test (purified protein derivative) in an individual who has never
had such a reaction suggests that a new infection has developed. Subsequent progression
to active tuberculosis can usually be prevented by 6 to 12 months of preventive therapy,
which should be considered for all persons who are newly infected. Nosocomial transmission
of tuberculosis is a significant threat to health care workers. Prevention should
include increased awareness of the disease, appropriate isolation and treatment of
infected patients, and a national program of education[75]
similar to that already mandated for blood-borne pathogens.[31]
