No abstract

The transmission and persistence of Mycobacterium tuberculosis within high risk populations is a threat to tuberculosis (TB) control. In the current study, we used whole genome sequencing (WGS) to decipher the transmission dynamics and microevolution of M. tuberculosis ON-A, an endemic strain responsible for an ongoing outbreak of TB in an urban homeless/under-housed population. Sixty-one M. tuberculosis isolates representing 57 TB cases from 1997 to 2013 were subjected to WGS. Sequencing data was integrated with available epidemiological information and analyzed to determine how the M. tuberculosis ON-A strain has evolved during almost two decades of active transmission. WGS offers higher discriminatory power than traditional genotyping techniques, dividing the M. tuberculosis ON-A strain into 6 sub-clusters, each defined by unique single nucleotide polymorphism profiles. One sub-cluster, designated ON-ANM (Natural Mutant; 26 isolates from 24 cases) was also defined by a large, 15 kb genomic deletion. WGS analysis reveals the existence of multiple transmission chains within the same population/setting. Our results help validate the utility of WGS as a powerful tool for identifying genomic changes and adaptation of M. tuberculosis.

While tuberculosis (TB) in Canadian cities is increasingly affecting foreign-born persons, homeless persons remain at high risk. To assess trends in TB, we studied all homeless persons in Toronto who had a diagnosis of active TB during 1998–2007. We compared Canada-born and foreign-born homeless persons and assessed changes over time. We identified 91 homeless persons with active TB; they typically had highly contagious, advanced disease, and 19% died within 12 months of diagnosis. The proportion of homeless persons who were foreign-born increased from 24% in 1998–2002 to 39% in 2003–2007. Among foreign-born homeless persons with TB, 56% of infections were caused by strains not known to circulate among homeless persons in Toronto. Only 2% of infections were resistant to first-line TB medications. The rise in foreign-born homeless persons with TB strains likely acquired overseas suggests that the risk for drug-resistant strains entering the homeless shelter system may be escalating.

In a P.1 COVID-19 outbreak in long-term-care, vaccine effectiveness against SARS-CoV-2 infection was 52.5% (95%CI 26.9-69.8%) in residents and 62.2% (95%CI, 2.3-88.3%) in staff. VE against severe illness was 78.6% (95%CI 47.9-91.2) in residents. Two of 19 vaccinated resident cases died. Outbreak management required both vaccination and infection control measures.

Background: In late 2016 and early 2017, a number of countries began reporting hepatitis A virus (HAV) outbreaks involving person-to-person transmission among men who have sex with men (MSM), people using illicit drugs and homeless or underhoused persons. Objective: To describe the epidemiology and public health response to an outbreak of HAV disproportionately affecting MSM in Toronto, Canada from January 2017 to November 2018. Methods: Following an increase in the number of cases of HAV in MSM being reported in other countries, enhanced surveillance was performed for all non-travel-related cases of HAV reported from June 1, 2017 to November 1, 2018, including a retrospective analysis of cases reported from January 2017 to June 2017. Descriptive analysis and viral sequencing were performed to describe person-to-person transmission patterns and target interventions. Control strategies included interventions to promote the uptake of preexposure HAV vaccination, including social media campaigns geared to MSM, messaging to healthcare providers and vaccine clinics. Results: Based on the outbreak case definitions, 52 confirmed and probable cases of HAV were identified. Over 80% of outbreak cases were male (n=43/52) and, among those for whom data were available, 64% (n=25/39) reported an MSM exposure. Data on hospitalization was available for 51 cases; 56% of confirmed cases (n=23/41) and 40% of probable cases (n=4/10) required hospitalization. Of the cases with serum samples that had HAV sequencing, 83% (n=30/36) had one of the three strains seen circulating in outbreaks among MSM internationally; 72% (n=26/36) were VRD_521_2016, which had been detected in recently reported European outbreaks among MSM. Targeted promotion of publicly-funded vaccination using social media platforms popular with MSM and targeted vaccine clinics were developed to promote HAV awareness and vaccine uptake among MSM. Conclusion: Outbreaks of HAV, attributed to person-to-person transmission of strains of HAV that disproportionately affected MSM and were likely to have been imported from international MSM outbreaks, have now occurred in Canada. Genetic sequencing of HAV, risk factor analysis of cases, monitoring trends of vaccine coverage in high-risk groups and initiation of vaccination campaigns that address barriers to HAV preexposure vaccine coverage in the MSM population may prevent future outbreaks.