CDC’s sample TB cases show hospitals how to assess risk

The Centers for Disease Control and Prevention (CDC) has provided examples of how to assess risk and determine if a health care setting should be classified as low or medium. Here are three excerpts from the draft TB guidelines, which are available at

  • A 150-bed hospital is located in a small city. During the preceding year, the hospital admitted two patients with a diagnosis of TB disease. One was admitted directly to an airborne infection isolation room, and one stayed on a medical ward for two days before being placed in an isolation room. A contact investigation of exposed health care workers by hospital infection control personnel in consultation with the state or local health department did not identify any health care-associated transmission. Low risk.
  • The setting is a large, publicly funded hospital in a major metropolitan area. The hospital admits an average of 150 patients with TB disease each year, comprising 35% of the city burden. The setting has a strong TB infection-control program (i.e., annually updates infection-control plan, fully implements infection-control plan, and the setting has enough airborne infection isolation rooms as described [in the draft guidelines]), and an annual M. tuberculosis infection test conversion rate among health care workers of 0.5%. The M. tuberculosis infection test conversion rate is the percentage of HCWs who have converted their tuberculin skin test or QuantiFERON test results within a specified time period calculated by dividing the number of M. tuberculosis infection test conversions among HCWs in the setting in a specified period of time (numerator) by the number of HCWs who received tuberculin skin tests or QuantiFERON tests in the setting over the same period of time (denominator) multiplied by 100. No evidence of health care-associated transmission is apparent. The hospital has strong collaborative links with the state or local health department. Medium risk, with close ongoing surveillance for episodes of transmission from unrecognized cases of TB disease, M. tuberculosis infection test conversions in HCWs as a result of health care-associated transmission, and specific groups or areas in which a higher risk for health care-associated transmission exists.
  • A hospital located in a large city admits 35 patients with TB disease per year and has an overall HCW M. tuberculosis infection test conversions, for a rate of 15%. All of the respiratory therapists who tested positive received medical evaluations, had TB disease excluded, were diagnosed with latent tuberculosis infection (LTBI), and were offered and completed a course of treatment for LTBI. None of the respiratory therapists had known exposures to M. tuberculosis outside the hospital. The problem evaluation revealed:

1. The respiratory therapists who converted had spent part of their time in the pulmonary function laboratory where induced sputum specimens were collected.

2. The ventilation in the laboratory was inadequate.

Potential ongoing transmission for the respiratory therapists (due to evidence of health care-associated transmission). The rest of the setting was classified as medium risk. To address the problem, booths were installed for sputum induction. No M. tuberculosis infection test conversions were noted at the repeat testing three months later, and the respiratory therapists were then reclassified back to medium risk.