Guide to the Application of Genotyping to Tuberculosis Prevention
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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.
Last Reviewed: 05/18/2008 Content Source: Division of Tuberculosis Elimination
National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention
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