Guide to the Application of Genotyping to Tuberculosis Prevention and Control

Tuberculosis Genotyping Case Studies: How TB Programs Have Used Genotyping

Identification of Nontraditional Transmission Settings

The Maryland Department of Health and Mental Hygiene described how universal genotyping can strengthen traditional TB control efforts. Maryland genotyped all of its M. tuberculosis isolates received during 1996 to 2000 and recently published the results (Cronin 2002).

Of 1,172 patients with genotyping results, genotypes from 436 matched those of at least one other patient in the state. Of the 436 clustered patients, 115 were thought to have acquired TB recently, and in 114 a setting of presumed transmission could be identified. Before the genotyping results were known, routine contact investigations identified epidemiologic links for 72 of the 114 patients (Table 2.3). During follow-up cluster investigations, additional information resulted in the identification of 42 patients with additional epidemiologic links.

Maryland’s cluster investigations, which were conducted after the genotyping results were available, helped to identify 30% more epidemiologic links than the original contact investigations. Many of these newly discovered epidemiologic links suggested that TB transmission occurred in settings that are often not asked about in routine contact investigations (e.g., homeless shelters, bars, churches, and nursing homes). The new information led TB program staff to screen previously unsuspected groups of persons.


Table 2.3. Transmission settings or relationships identified by either routine contact investigations or by cluster investigations for 114 patients with recently acquired tuberculosis — Maryland, 1996–2000.

Traditional

Transmission setting or relationship Total patients with known setting Setting identified by routine contact investigation (%) Setting identified only by cluster investigation (%)
Household 28 25 ( 89) 3 ( 11)
Close relative 13 13 (100) 0
Close friend 17 11 ( 65) 6 ( 35)
Total traditional 58 49 ( 84) 9 ( 16)

Nontraditional*

Transmission setting or relationship Total patients with known setting Setting identified by routine contact investigation (%) Setting identified only by cluster investigation (%)
Hospital 10 5 ( 50) 5 ( 50)
Other workplace 6 6 (100) 0
Social club 11 7 ( 64) 4 ( 36)
Homeless shelter 5 0 5 (100)
Bar 10 1 ( 10) 9 ( 90)
Prison or jail 5 3 ( 60) 2 ( 40)
Store 2 0 2 (100)
Church 2 0 2 (100)
Nursing home 2 0 2 (100)
School 1 0 1 (100)
Ship 1 1 (100) 0
Mortuary 1 0 1 (100)
Total nontraditional 56 23 ( 41) 33 ( 59)

* The definition of nontraditional settings of transmission used by Maryland is not identical to the one used in Table 4.2.

Page last reviewed: September 1, 2012