Investigation of two cases of <i>Mycobacterium chelonae</i> infection in haemato-oncology patients using whole genome sequencing and a potential link to the hospital water supply

BackgroundHaemato-oncology patients are at increased risk of infection from atypical mycobacteria such as Mycobacterium chelonae which are commonly found in both domestic and hospital water systems.AimsTo describe the investigation and control measures following two patient cases of M. chelonae and positive water samples in our hospital.MethodsWater testing was undertaken from outlets, storage tanks and mains supply. We utilised whole genome sequencing (WGS) to compare patient and positive water samples. We describe the subsequent infection control measures implemented.FindingsThe WGS results showed two main populations of M. chelonae within the group of sampled isolates. The results showed that the patient strains were unrelated to each other but that the isolate from one patient was closely related to environmental samples from water outlets, supporting nosocomial acquisition.ConclusionsWe describe the utility of WGS in the investigation of two patient cases of M. chelonae, and positive water samples from a hospital water supply. We discuss relevant control measures and the potential for chemical dosing of water systems to enhance proliferation of atypical mycobacteria.</p

Characterising transmission of a tuberculosis genotype in Scotland: a qualitatibe approach to social network enquiry

Setting: Contact investigation resulting from specimens sent to the Scottish Mycobacteria Reference Laboratory. Objective: To characterise patients and types of exposures associated with transmission of a prevalent Mycobacterium tuberculosis genotype in Scotland. Design: A combined approach using molecular epidemiology and semi-structured patient interviews for social network enquiry. Results: We investigated social connections between 64 patients diagnosed between 1994 and 2004. Fifty-five per cent had ≥1 identifiable contact. One third (n = 14, 32.6%) of the 43 epidemiological links detected were discerned as a result of patient interviews and were not previously recorded on surveillance reports, nor recognised by nurse specialists (all were non-household contacts). Sixteen putative sites of exposure were identified, 11 were public houses. Rather than a single-source outbreak, eight pockets of transmission were identified, the largest involving UK-born alcohol-misusing males frequenting several public houses. Conclusions: Using a standardised approach to explore themes around which individuals may have been exposed to TB resulted in the detection of previously unrecognised epidemiological links. Epidemiological data obtained from cluster investigations, e.g., risk and social behaviours that increase the risk of infection and sites of putative exposure, can enhance the development of more appropriate questions for the contact tracing interview