Tuberculosis contact investigations: outcomes in selected areas of the United States, 1999.

SETTING: Twenty-nine United States jurisdictions. OBJECTIVE: To determine yields of tuberculosis (TB) contact investigations. METHODS: Health departments within the jurisdictions reported counts and outcomes from routine contact investigations for cases reported in 1999. RESULTS: The 29 jurisdictions reported 9199 TB cases, 51.9% of the US and Puerto Rico 1999 total, and listed 67585 contacts. While 571 (10.6%) of 5405 pulmonary cases confirmed by sputum bacteriology had no contacts listed, 13904 contacts were listed for other cases that were unlikely to be contagious. Diagnostic evaluation was completed for 56100 contacts (83.0%), with 561 TB cases found. Of 13083 contacts found to have latent TB infection, 5746 (44.5%) completed treatment to prevent TB. Loss to follow-up and self-discontinuation of treatment accounted for 70% of reasons why treatment was not completed. CONCLUSION: Contact investigations capture substantial numbers of TB cases and latent TB infections, but the impact on prevention is limited by the poor treatment rates for infected contacts. Contacts should be sought for each potentially contagious TB case; why so many contacts are sought for cases who are unlikely to be contagious needs to be determined.

The role of the public health department in tuberculosis.

The role of the public health department in TB is a critical component of the overall TB control effort. This article illustrates both the traditional public health methods of surveillance, containment and prevention, and some of the newer strategies being employed to address TB control in today's multifaceted environment. It shows that controlling TB will require an intensification of collaborative efforts between public, private and community providers. In particular, the role of public health and health care workers in institutional settings is emphasized as it relates to shared community efforts. In light of the recent outbreaks of drug-resistant disease and the associated dramatic increasing TB morbidity and mortality, the need for these partnerships is urgent. Given the legal mandate for TB control, health departments will continue to play a major role in the elimination of this disease. The deterioration of these public health services, however, will require immediate attention lest the very foundation of TB control be allowed to crumble.

Airborne infection. Theoretical limits of protection achievable by building ventilation.

Of 67 office workers 27 (40%) had documented tuberculin skin test conversions after an estimated 4-wk exposure to a coworker with cavitary tuberculosis. Worker complaints for more than 2 yr before the tuberculosis exposure prompted investigations of air quality in the building before and after the tuberculosis exposure. Carbon dioxide concentrations in many parts of the building were found to be above recommended levels, indicating suboptimal ventilation with outdoor air. We applied a mathematical model of airborne transmission to the data to assess the role of building ventilation and other transmission factors. We estimated that ventilation with outside air averaged about 15 feet 3/min (cfm) per occupant, the low end of acceptable ventilation, corresponding to CO2 levels of about 1,000 ppm. The model predicted that at 25 cfm per person 18 workers would have been infected (a 33% reduction) and at 35 cfm, a level considered optimal for comfort, that 13 workers would have been infected (an additional 19% reduction). Further increases in outdoor air ventilation would be impractical and would have resulted in progressively smaller increments in protection. According to the model, the index case added approximately 13 infectious doses (quanta) per hour (qph) to the office air during the exposure period, 10 times the average infectiousness reported in a large series of tuberculosis cases. Further modeling predicted that as infectiousness rises, ventilation would offer progressively less protection. We conclude that outdoor air ventilation that is inadequate for comfort may contribute to airborne infection but that the protection afforded to building occupants by ventilation above comfort levels may be inherently limited, especially when the level of exposure to infection is high.