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TB Notes 2, 1999

Update from the Surveillance and Epidemiology Branch

Evaluation of Contact Investigation Procedures, Practices, and Results

Treating individuals recently infected with M. tuberculosis is a cornerstone of efforts to eliminate tuberculosis (TB) in the United States. Since approximately one third of contacts to patients with active pulmonary TB become infected following exposure, they represent a high-risk group for TB. Thus, conducting contact investigations to identify and screen persons potentially exposed to infectious cases of TB is essential to the TB elimination effort. A retrospective study was conducted in 1998 to characterize current contact investigation procedures, practices, and results at study sites in Colorado, Maryland, Massachusetts, Mississippi, and New Jersey. Study sites were chosen through a competitive agreement process. Health department records were reviewed for culture-positive pulmonary TB cases among persons ³ 15 years of age reported in 1996 for each of the five study areas, and for all identified contacts of these cases. Preliminary results of this study are summarized in this report.

A total of 6,991 contacts were identified for 360 reported TB cases. The mean and median number of contacts identified per case were 19 and 5, respectively (range, 0 - 720). No contacts were identified for 10% of all cases. Among the contacts identified, 47% did not complete tuberculin skin test (TST) screening: 15% were not screened and 32% had an initial TST but no follow-up TST ³ 10 weeks postexposure. Among the contacts screened, 1% had active TB at the time of investigation, 4% had initial negative and subsequent positive TSTs (converters), 18% had initial positive TSTs with no prior test result, and 77% had negative TSTs > 10 weeks after last exposure. Only 71% of all contacts with newly documented positive TSTs (persons with initial positive TSTs and converters) were known to have had treatment of latent infection recommended, and only 32% were known to have completed a full course of treatment of infection. Contacts < 15 years of age, TST converters, and close contacts were more likely to have treatment of infection recommended, and TST converters were more likely to complete a full course of treatment of infection. For those for whom treatment of infection was recommended, persons in all age groups were equally likely to complete therapy. Birthplace was missing for nearly half of all contacts. Of persons with known birthplace, U.S. and foreign-born contacts were equally likely to have treatment of infection recommended, and equally likely to complete > 6 months of therapy.

Definitions of a contact or a close contact varied considerably between study areas. In addition, most study areas had no standard criteria for expanding contact investigations beyond the "inner circle" of contacts. The types of data being collected during contact investigations also varied considerably between study areas. Furthermore, a number of factors associated with case infectiousness, contact susceptibility to TB infection, and contact risk of progression to TB disease were missing from most case and contact health department records.

Findings from this study highlight the need for 1) improvement in the contact investigation process to ensure that all contacts are identified, all identified contacts are completely screened, and all eligible contacts complete a full course of preventive therapy; 2) written documentation of key case and contact data; 3) a set of standard indicators so that health departments can monitor the effectiveness of each step in the contact investigation process; 4) standard definitions for what constitutes a contact and a close contact; 5) standard criteria for expanding contact investigations; and 6) definitions for the extent of contact investigation needed in various epidemiologic settings. A prospective study is needed to provide all the information necessary to improve and standardize the contact investigation process. CDC is sponsoring such a study in collaboration with the Colorado Department of Health, Denver Metro TB Control, the Maryland Department of Health and Mental Hygiene, the Mississippi State Department of Health, the New Jersey Department of Health and Senior Services, and the New Jersey Medical School National Tuberculosis Center.

—Reported by Mary Reichler, MD
Division of TB Elimination


Released October 2008
Centers for Disease Control and Prevention
National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention
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