Universal Genotyping for Tuberculosis Prevention Programs: a 5-Year Comparison with On-Request Genotyping

Abstract

Prospective universal genotyping of tuberculosis (TB) isolates is used by many laboratories to detect clusters of cases and inform contact investigations. Prior to universal genotyping, most TB prevention programs genotyped isolates on request only, relying on requests from public health professionals whose knowledge of a patient's clinical, demographic, and epidemiological characteristics suggested potential transmission. To justify the switch from on-request to universal genotyping-particularly in the public health domain, with its limited resources and competing priorities-it is important to demonstrate the additional benefit provided by a universal genotyping program. We compared the clustering patterns revealed by retrospective 24-locus mycobacterial interspersed repetitive unit-variable-number tandem repeat genotyping of all culture-positive isolates over a 5-year period to the patterns previously established by our genotyping-on-request program in the low-incidence setting of British Columbia, Canada. We found that 23.8% of isolates were requested during the study period, and while requested isolates had increased odds of belonging to a genotype cluster (adjusted odds ratio, 2.3; 95% confidence interval, 1.5 to 3.3), only 54.6% clustered with the requested comparator strain. Universal genotyping revealed 94 clusters ranging in size from 2 to 53 isolates (mean = 5) and involving 432 individuals. On-request genotyping missed 54 (57.4%) of these clusters and 130 (30.1%) clustered individuals. Our results underscore that TB patient networks are complex, with unrecognized linkages between patients, and a prospective province-wide universal genotyping program provides an informative, bias-free tool to explore transmission to a degree not possible with on-request genotyping.

Keywords: MIRU-VNTR genotyping; program assessment; tuberculosis.

FIG 1

Bubble plot of the proportion of each cluster requested for genotyping to confirm or refute transmission, with the average cluster growth per quarter in BC from 2009 to 2013. Growing clusters had a minimum of three persons in the cluster over the study period. Bubbles are colored to indicate the predominant birthplace (≥50%) of the individuals in each cluster and sized to represent the total number of genotypically clustered cases. Cluster identifiers are indicated for clusters with five or more patients.

FIG 2

Annual cluster growth and overall cluster size for all clusters with three or more persons in BC from 2009 to 2013. Bars are colored by genotype requested (yes/no). Twenty-four-locus MIRU-VNTR genotyping cluster identifiers (MClustID) in bold italics represent clusters that are composed of predominantly Canadian-born persons.