Mycobacterium tuberculosis DNA Fingerprinting from Epidemiologically Linked Case Pairs
Authors: Bennett, Diane E.; Onorato, Ida M.; Ellis, Barbara A.; Crawford, Jack T.; Schable, Barbara; Byers, Robert; Kammerer, J. Steve; Braden, Christopher R.;
Publisher: CDC Open Access
DNA fingerprinting was used to evaluate epidemiologically linked case pairs found during routine tuberculosis (TB) contact investigations in seven sentinel sites from 1996 to 2000. Transmission was confirmed when the DNA fingerprints of source and secondary cases matched. Of 538 case pairs identified, 156 (29%) did not have matching fingerprints. Case pairs from the same household were no more likely to have confirmed transmission than those linked elsewhere. Case pairs with unconfirmed transmission were more likely to include a smear-negative source case (odds ratio [OR] 2.0) or a foreign-born secondary case (OR 3.4) and less likely to include a secondary case less than 15 years old (OR 0.3). Our study suggests that contact investigations should focus not only on the household but also on all settings frequented by an index case. Foreign-born persons with TB may have been infected previously in high-prevalence countries; screening and preventive measures recommended by the Institute of Medicine could prevent TB reactivation in these cases.
Investigating persons who have had close contact with tuberculosis (TB) cases is an essential element of public health programs to control and eliminate TB (1,2). These contact investigations are done primarily to discover persons who may require treatment for latent TB infection and also to find and treat additional persons with TB. While not usually highly contagious, TB is generally transmitted to persons who have shared indoor air space frequently or for a long period of time with a person who is infectious (3). Factors that may influence transmission include prolonged hours of contact during the infectious period, close proximity to the person with TB, and lack of ventilation and ultraviolet light in a shared environment. Generally, close contacts who live with a person identified with active TB or who habitually spend time indoors in close proximity to this person are investigated first. If no evidence of TB transmission is found in these close contacts, the investigation ceases. If transmission has occurred, the investigation may be extended. The “stone-in-the-pond” principle, a technique in which concentric circles of contact persons around the case are sequentially investigated, is practiced in many countries