Detailed characterisation of the tuberculosis epidemic in Western Sydney: a descriptive epidemiological study

Sustained transmission over two decades of a previously unrecognised MPT64 negative Mycobacterium tuberculosis strain in Queensland, Australia: a whole genome sequencing study

Background

MPT64 is a key protein used for Mycobacterium tuberculosis (MTB) complex strain identification. We describe protracted transmission of an MPT64 negative MTB strain in Queensland, Australia, and explore genomic factors related to its successful spread.

Methods

All MPT64 negative strains identified between 2002 and 2022 by the Queensland Mycobacteria Reference Laboratory, and an additional 2 isolates from New South Wales (NSW), were whole genome sequenced. Bayesian modelling and phylogeographical analyses were used to assess their evolutionary history and transmission dynamics. Protein structural modelling to understand the putative functional effects of the mutated gene coding for MPT64 protein was performed.

Findings

Forty-three MPT64 negative isolates were sequenced, belonging to a single MTB cluster of Lineage 4.1.1.1 strains. Combined with a UK dataset of the same lineage, molecular dating estimated 1990 (95% HPD 1987-1993) as the likely time of strain introduction into Australia. Although the strain has spread over a wide geographic area and new cases linked to the cluster continue to arise, phylodynamic analysis suggest the outbreak peaked around 2003. All MPT64 negative strains had a frame shift mutation (delAT, p.Val216fs) within the MPT64 gene, which confers two major structural rearrangements at the C-terminus of the protein.

Interpretation

This study uncovered the origins of an MPT64 negative MTB outbreak in Australia, providing a richer understanding of its biology and transmission dynamics, as well as guidance for clinical diagnosis and public health action. The potential spread of MPT64 negative strains undermines the diagnostic utility of the MPT64 immunochromatographic test.

Funding

This study was funded from an operational budget provided to the Queensland Mycobacterium Reference Laboratory by Pathology Queensland, Queensland Department of Health.

Tuberculosis in elderly Australians: a 10-year retrospective review

Objective

This report describes the epidemiology of active tuberculosis (TB) in elderly Australians (≥ 65 years) with analysis of the factors associated with TB disease and successful treatment outcomes.

Methods

A retrospective study of TB cases reported to the National Notifiable Diseases Surveillance System over a 10-year period from 2011 to 2020 was conducted. Cases were stratified by sex, age, risk factors, drug resistance, treatment type and outcome. Notification rates and incidence rate ratios with 95% confidence intervals were calculated and factors associated with treatment success analysed using multivariable logistic regression.

Results

A total of 2231 TB cases among elderly people were reported over the study period, with a 10-year mean incidence rate of 6.2 per 100 000 population. The median age of cases was 75 years (range 65-100 years); most were male (65%) and born overseas (85%). Multivariable analysis found that successful treatment outcome was strongly associated with younger age, while unsuccessful treatment outcome was associated with being diagnosed within the first 2 years of arrival in Australia, ever having resided in an aged-care facility and resistance to fluoroquinolones.

Discussion

Compared to other low-incidence settings in the Western Pacific Region, TB incidence in elderly people is low and stable in Australia, with most cases occurring among recent migrants from TB-endemic settings. Continued efforts to reduce TB importation and address migrant health, especially among elderly people, are important.

Chronic Pulmonary Aspergillosis: Burden, Clinical Characteristics and Treatment Outcomes at a Large Australian Tertiary Hospital

Chronic pulmonary aspergillosis (CPA) is a fungal lung infection associated with high morbidity and mortality. Yet, it remains under-recognized worldwide, with few Australian clinical data available. This retrospective study aimed to investigate CPA at a major tertiary referral hospital in Sydney. We identified patients having International Classification of Diseases (ICD-10) codes for “aspergillosis” and/or positive respiratory microbiology samples for Aspergillus species from January 2012–December 2018 at Westmead Hospital. Eligible cases were classified using European Respiratory Society 2016 CPA guidelines. We diagnosed 28 CPA patients: median age 60 years (IQR: 57–66), with 17 (60.7%) being males. Most had chronic cavitary pulmonary aspergillosis phenotype (n = 17, 60.7%). Twenty-three patients had outcomes data returned. Nineteen (82.6%) received antifungal therapy (median duration: 10.5 months (IQR: 6.5–20.7)). Eight (34.7%) patients received <6 months of antifungals, including three (38%) deaths. Two (13%) patients receiving ≥6 months of antifungals died. Chronic obstructive pulmonary disease (COPD) (n = 9, 32.1%) was the leading predisposing factor for CPA in our cohort. This contrasts with the global picture, where prior tuberculosis generally predominates, but is similar to findings from other high-income countries. Nevertheless, further larger-scale studies are required to determine whether these results are generalizable to the wider Australian population.

Migration and descent, adaptations to altitude and tuberculosis in Nepalis and Tibetans

Background

High rates of tuberculosis (TB) in migrants from Tibet and Nepal have been documented for over 120 years and were previously ascribed to poor living conditions in the places of settlement. Adaptations to altitude involving genes in the Hypoxia-Inducible Factor pathway are present in 90–95% of Tibetans and in Nepalis these allele frequencies increase by 17% with each 1000 m increase in altitude.

Methods

We calculated the incidence of TB by country of origin in immigrants from South and East Asia in New South Wales (NSW), Australia between 2004 and 2018, and compared disease severity, site of infection, evidence of local transmission and prevalence of latent TB, among these groups.

Results

The incidence of active TB was consistently higher among 30 000 Nepalese and 1000 Tibetans than among all other immigrants to NSW. Nepal was the only country of origin where TB incidence in immigrants was not significantly lower than the reported TB incidence in the country of origin.

Conclusions and implications

High rates of TB among Nepalese and Tibetan immigrants in Australia are unlikely to be attributable to pre-existing disease or local acquisition. Phenotypic effects of high-altitude adaptations may include a dampening of inflammatory responses to hypoxia, an effect unmasked by descent to a normoxic environment. A corollary of these findings may be that hypoxia-induced inflammation limits TB progression, reconfirming previous explanations for the apparent efficacy of high-altitude sanatoria. If vindicated by subsequent research, these provisional findings could open new avenues into preventive and host-directed interventions for tuberculosis.

Lay Summary

The incidence of tuberculosis among Nepalese immigrants to Australia and other people of Tibetan heritage who migrate to lower altitudes is very high. In these screened populations, pre-existing active TB or locally acquired infection are unlikely explanations. We suggest that adaptations to altitude combined with descent to higher oxygen levels in air at sea level may be contributing factors.