Using genotyping to delineate tuberculosis transmission in long-term care facilities: single facility 4-year experience

Reducing tuberculosis transmission by genotype-based contact tracing coupled with public health containment measures: a case study during the COVID-19 pandemic in Taiwan

This study aimed to estimate the effectiveness of genotype-based contact tracing coupled with public health and social containment measures (PHSMs) in reducing tuberculosis (TB) transmission during the COVID-19 pandemic. Patients suspicious of recent TB infection from index cases were traced by genotyping method between 2017 and 2021. To make allowance for TB cases attributed to reactivation, TB cases identified from the genotype-based contact tracing group were compared to those from the underlying population via the notifiable nationwide system without genotyping. The relative changes (ratios) in TB cases before and during the pandemic between the two groups were leveraged to estimate the effectiveness of PHSMs following genotype-based contact tracing, taking into account demographic features and geographic variation, with a multivariable Poisson regression model. Before the pandemic, we identified 42 of 133 (31.6%) sputum culture-positive index (SCI) patients via 344 genotype-matched clustered TB cases. During the pandemic, 11 of 70 (15.7%) SCI patients were linked to 36 clustered cases. The annual average of TB-clustered patients for the genotype-based contact tracing group decreased by 84.3%, whereas the corresponding figure for the comparator decreased by 18.5%. The adjusted relative risk of 0.19 (95% CI 0.14-0.28) gave an 81% TB transmission reduction after controlling for extraneous factors. Genotype-based contact tracing coupled with PHSMs significantly reduced TB transmission. Our findings from the pandemic period demonstrate that a molecular epidemiological approach with public health containment measures will enable a moderate-burden TB country to reach the WHO End TB targets by 2035.IMPORTANCEThe extent to which COVID-19 public health and social measures reduced tuberculosis transmission remains unclear. We elucidated the recent tuberculosis infection with a novel genotype-based contact tracing from 2017 to 2021. These patients were recruited as the contact tracing group in contrast to the comparison group of tuberculosis cases from the general population via the notifiable nationwide system without genotyping. The relative changes in tuberculosis cases before and during the pandemic between the contact tracing group and the comparison group were used to estimate the effectiveness of reducing tuberculosis transmission. We found a significant 81% reduction in tuberculosis transmission during the first 2 years of the pandemic. This finding demonstrates that a molecular epidemiological approach with public health containment measures will enable a moderate-burden tuberculosis country to reach the End TB targets by 2035.

Define SNP thresholds for delineation of tuberculosis transmissions using whole-genome sequencing

For facilitating tuberculosis (TB) control, we used a whole-genome sequencing (WGS)-based approach to delineate transmission networks in a country with an intermediate burden of TB. A cluster was defined as Mycobacterium tuberculosis isolates with identical genotypes, and an outbreak was defined as clustered cases with epidemiological links (epi-links). To refine a cluster predefined using space oligonucleotide typing and mycobacterial interspersed repetitive unit variable tandem repeat typing, we analyzed one pansusceptible TB (C1) and three multidrug-resistant (MDR)-TB (C2-C4) clusters from different scenarios. Pansusceptible TB cluster (C1) consisting of 28 cases had ≤5 single nucleotide polymorphisms (SNPs) difference between their isolates. C1 was a definite outbreak, with cases attending the same junior high school in 2012. Three MDR-TB clusters (C2-C4) with distinct genotypes were identified, each consisting of 12-22 cases. Some of the cases had either ≤5 or ≤15 SNPs difference with clear or probable epi-links. Of note, even though WGS could effectively assist TB contact tracing, we still observed missing epi-links in some cases within the same cluster. Our results showed that thresholds of ≤5 and ≤15 SNPs difference between isolates were used to categorize definite and probable TB transmission, respectively. Furthermore, a higher SNP threshold might be required to define an MDR-TB outbreak. WGS still needs to be combined with classical epidemiological methods for improving outbreak investigations. Importantly, different SNP thresholds have to be applied to define outbreaks.

IMPORTANCE

TB is a chronic disease. Depending on host factors and TB burden, clusters of cases may continue to increase for several years. Conventional genotyping methods overestimate TB transmission, hampering precise detection of outbreaks and comprehensive surveillance. WGS can be used to obtain SNP information of M. tuberculosis to improve discriminative limitations of conventional methods and to strengthen delineation of transmission networks. It is important to define the country-specific SNP thresholds for investigation of transmission. This study demonstrated the use of thresholds of ≤5 and ≤15 SNPs difference between isolates to categorize definite and probable transmission, respectively. Different SNP thresholds should be applied while a higher cutoff was required to define an MDR-TB outbreak. The utilization of SNP thresholds proves to be crucial for guiding public health interventions, eliminating the need for unnecessary public health actions, and potentially uncovering undisclosed TB transmissions.

Bovine tuberculosis in Taiwan, 2008-2019

Bovine tuberculosis (bTB) is a zoonosis caused by Mycobacterium bovis. The impact of bTB on global TB control has been underestimated. We adopted the One Health approach to human bTB surveillance in Taiwan. Of 20,972 human TB cases, 202 (1.0%) were bTB, 78.2% were in males, 85.1% were new cases, 83.2% were pulmonary TB, and most were in Central (52.5%) and Southern (24.8%) Taiwan. Only 18.8% of bTB patients had known animal contact. Of the 202 human M. bovis strains, 100% were resistant to pyrazinamide (PZA), 30.2% were concurrently resistant to isoniazid (INH) and 2.0% were multidrug resistant, defined as being resistant to at least INH and rifampin. Whereas, of the 22 animal M. bovis strains, 100% and 22.7% were resistant to PZA and INH, respectively. Seven spoligotypes and 25 mycobacterial interspersed repetitive unit genotypes were identified. The predominant genotype, SB0265, was also prevalent in livestock. Notably, six animal-specific M. bovis genotypes were identified. bTB differential diagnosis and drug resistance detection are crucial for TB control. Comprehensive surveillance and human-animal interface investigations are needed.

Ambulatory independence is associated with higher incidence of latent tuberculosis infection in long-term care facilities in Taiwan

BACKGROUND/PURPOSE

Tuberculosis (TB) in the elderly population remains a major challenge in areas with intermediate disease burden like Taiwan. Despite the increasing burden and high risks of TB in the elderly population, particularly those living in long-term care facilities (LTCFs), diagnostic testing for latent tuberculosis infection (LTBI) has not been carefully evaluated in this group. This study aimed to investigate the prevalence and predictors of LTBI in older adults living in LTCFs.

METHODS

Older adults living in seven LTCFs in Taiwan were prospectively enrolled between January and July 2017. Interferon-gamma release assay (IGRA) through QuantiFERON-TB Gold In-tube was used to determine presence of LTBI. Predictors for LTBI were analyzed.

RESULTS

A total of 258 participants were enrolled, including 240 older residents (mean age, 81.6 years; male, 51.2%) and 18 employees (mean age, 64.8 years; male, 22.2%). The proportion of independent status in ambulation assessments significantly declined with aging (p < 0.001). The IGRA-positivity rate in LTCFs was 31.4% (81/258), which consisted of 73 (30.4%) residents and 8 (44.4%) employees. The IGRA results were different with respect to the ambulation status (p = 0.052). In the multivariate logistic regression analysis, the only independent predictor of LTBI among older adults in LTCFs was independent ambulation (odds ratio, 2.16; 95% confidence interval, 1.09-4.28; p = 0.027).

CONCLUSIONS

There was a high prevalence of LTBI among older adults in LTCFs in Taiwan. Independent ambulation was the only independent predictor of LTBI.