Trends in microbiology testing in Australian long-term care facilities: national cohort study

Microbiology testing can guide infectious disease management and antimicrobial selection, including for older people living in long-term care facilities (LTCFs), who are at high risk of infectious diseases. However, insufficient and excessive microbiology testing can contribute to inappropriate antimicrobial use. The study examined national trends, co-testing, and LTCF variation in microbiology testing.

This national repeated cross-sectional study included individuals aged 65-105 years residing in Australian LTCFs between 2009 and 2019. The annual age and sex standardised (i) proportion of individuals with a microbiology test and (ii) number of tests performed/100 resident-years were determined. Annual changes were estimated using adjusted rate ratios (aRRs) with 95% confidence intervals (CIs) from Poisson or negative binomial models. Co-testing and LTCF variation in 2019 were also evaluated.

Among the 547,067 studied residents, the median age at study entry was 84 years and 65.8% were women. Proportion of microbiology testing increased from 50.2% (95%CI 49.8-50.5) in 2009 to 59.4% (95%CI 59.0-59.7) in 2019 (aRR 1.02, 95%CI 1.01-1.02). Urine tests were the most frequently requested microbiology test, increasing from 40.9% (95%CI 40.5-41.2) to 44.9% (95%CI 44.5-45.2) during 2009-2019 (aRR 1.01, 95%CI 1.01-1.01). Nucleic acid amplification tests (NAATs) increased from 3.4% (95%CI 3.3-3.5) to 17.9% (95%CI 17.7-18.1) (aRR 1.21, 95%CI 1.21-1.21). In 2019, there were 1,614 (58.6%) LTCFs where the adjusted proportion of microbiology testing fell within the 95%CI range around the population mean. Faecal, Cryptosporidium/Giardia, and Clostridioides difficile/C.toxin tests were commonly performed concurrently with NAATs.

Over an 11-year period, microbiology testing increased. Eight out of ten residents were tested at least once during their LTCF stay, and considerable facility variation in testing was observed. Diagnostic stewardship targeting commonly requested microbiology tests (e.g., urine tests) could optimise antimicrobial use in LTCFs.