Objective: To investigate an outbreak of tuberculosis, determine the number of active cases and infections, and examine efforts to control the spread of disease.
Setting: A small town in Maine, in which no cases of tuberculosis had been reported in the previous 3 years.
Design: Epidemiologic investigation of an outbreak of tuberculosis infection and disease.
Measurements: A patient with an active case of tuberculosis was defined as a resident of the town or the surrounding area or an employee of the local shipyard who had a culture of sputum or tissue that was positive for Mycobacterium tuberculosis between June 1989 and May 1992. A case of tuberculous infection was defined as a positive tuberculin skin test result in a person with no previous positive test result.
Results: 21 active cases of tuberculosis occurred among shipyard workers and persons residing in the affected community between 1989 and 1992. One patient was the source of the outbreak; 8 months lapsed between the onset of this patient's illness and appropriate diagnosis and treatment. The M. tuberculosis strains isolated from this patient and from six other patients belonged to phage type I, auxiliary 14. All isolates were susceptible to drug treatment. Of 9898 persons who were tested, 697 (7%) were newly infected. Because isoniazid prophylaxis was not routinely offered to infected persons older than 35 years of age, only 341 (49%) infected persons completed isoniazid prophylaxis.
Conclusions: Many secondary cases of tuberculosis occurred throughout this small Maine community because of delayed diagnosis and treatment of the source patient, delayed outbreak investigation, and failure to promote isoniazid prophylaxis to all persons infected during the outbreak. Aggressive efforts to identify persons with new infection are of limited value in controlling tuberculosis unless they are accompanied by an equally aggressive use of isoniazid prophylaxis.