Mycobacterium tuberculosis transmission over an 11-year period in a low-incidence, urban setting

The problem with defining foreign birth as a risk factor in tuberculosis epidemiology studies

OBJECTIVE

To examine how stratifying persons born outside Canada according to tuberculosis (TB) incidence in their birth country and other demographic factors refines our understanding of TB epidemiology and local TB transmission.

BACKGROUND

Population-level TB surveillance programs and research studies in low incidence settings often report all persons born outside the country in which the study is conducted as "foreign-born"-a single label for a highly diverse population with variable TB risks. This may mask important TB epidemiologic trends and not accurately reflect local transmission patterns.

METHODS

We used population-level data from two large cohorts in British Columbia (BC), Canada: an immigration cohort (n = 337,492 permanent residents to BC) and a genotyping cohort (n = 2290 culture-confirmed active TB cases). We stratified active TB case counts, incidence rates, and genotypic clustering (an indicator of TB transmission) in BC by birth country TB incidence, age at immigration, and years since arrival.

RESULTS

Persons from high-incidence countries had a 12-fold higher TB incidence than those emigrating from low-incidence settings. Estimates of local transmission, as captured by genotyping, versus reactivation of latent TB infection acquired outside Canada varied when data were stratified by birthplace TB incidence, as did patient-level characteristics of individuals in each group, such as age and years between immigration and diagnosis.

CONCLUSION

Categorizing persons beyond simply "foreign-born", particularly in the context of TB epidemiologic and molecular data, is needed for a more accurate understanding of TB rates and patterns of transmission.

Shortening Isolation of Patients With Suspected Tuberculosis by Using Polymerase Chain Reaction Analysis: A Nationwide Cross-sectional Study

BACKGROUND

Isolation of patients suspected for pulmonary tuberculosis is guided by serial sputum smears. This can result in isolation for days for patients with noncontagious tuberculosis. To determine whether a single sample negative for Mycobacterium tuberculosis complex at polymerase chain reaction (PCR) can guide isolation.

METHODS

We retrospectively evaluated sputum samples analyzed for M. tuberculosis complex at the International Reference Laboratory of Mycobacteriology, Copenhagen, Denmark in 2002-2011. We selected culture-confirmed tuberculosis cases with ≥3 samples within 14 days before or after the initial culture-positive sample. We repeated the process for those with ≥2 samples within 28 days. The primary outcome was PCR-negative, smear-positive patients.

RESULTS

We included 53 533 sputum samples from 20 928 individuals; 1636 had culture-confirmed tuberculosis. Of these, 856 had ≥3 sputum samples analyzed within the 28 days, and 482 had ≥1 PCR result. Nine patients (2.5% of smear-positive patients) were smear positive/PCR negative; 8 of the 9 had a smear-positive result in only 1 of 3 samples, and 5 had a low smear grade. Of 722 patients with 2 samples, 7 (1.3% of smear-positive patients) were smear positive/PCR negative. Overall, none were smear positive for the sample that produced the negative PCR result.

CONCLUSIONS

Primary PCR identified >97% of serial smear-positive cases. The majority of the missed cases had low-grade smears. Nevertheless, the occurrence of smear-positive/PCR-negative cases underlines the importance of increasing the quantity and quality of samples. Moreover, it is important that samples analyzed with PCR are cultured, owing to higher-sensitivity drug susceptibility testing, differential diagnosis, and surveillance.

The impact of tuberculosis on health utility: a longitudinal cohort study

PURPOSE

To estimate health utility derived from the Short Form-36 (SF-36) questionnaire and Standard Gamble instrument for persons diagnosed and treated for tuberculosis (TB) disease, those diagnosed and treated for latent TB infection (LTBI), and those screened but not treated for TB disease or LTBI over the year following their diagnosis/initial assessment.

METHODS

Participants were recruited at two Montreal hospitals (2008-2011) and completed the SF-36 and Standard Gamble at baseline and at follow-up visits 1, 2, 4, 6, 9, and 12 months thereafter. SF-6D health utility scores were derived from SF-36 responses. Linear mixed models were used to compare mean health utility at each evaluation and changes in health utility between participants treated for TB disease, those treated for LTBI, and those in the control group.

RESULTS

Of the 263 participants, 48 were treated for TB disease, 105 for LTBI, and 110 were control participants. Fifty-four percent were women, mean age was 35 years, and 90% were foreign-born. Participants treated for TB disease reported worse health utility compared with control participants at the baseline visit (mean SF-6D: 0.69 vs. 0.81; mean Standard Gamble: 0.64 vs. 0.96). They reported successive improvement at months 1 and 2 that was then sustained throughout follow-up. Health utility reported by participants treated for LTBI and control participants was comparable throughout the study.

CONCLUSION

Treatment for TB disease had a substantial negative impact on health utility, particularly during the first 2 months of treatment. However, treatment for LTBI did not have a substantial impact.