Varicella-zoster-virus-related hospital episodes increasingly coded concurrently for varicella and zoster, Australia,...

Accurate varicella (chickenpox) and zoster (shingles)-coded hospitalisation data are important for disease surveillance and to examine the impact of immunisation programs. Varicella and zoster generally occur many years apart, with hospital episodes coded for both diseases concurrently implausible.

We aimed to describe varicella-zoster virus-related hospital episodes coded for both varicella and zoster or postherpetic neuralgia ('dual-coded') in Australia.

Hospital episodes with ICD-10-AM code for varicella, zoster or postherpetic neuralgia between 2002 and 2021 were included and examined for dual-code assignment of both varicella and zoster or postherpetic neuralgia code, by principal diagnosis, age group and state/territory. Trends over time were assessed with segmented linear or negative binomial regression models.

The proportion of hospital episodes with principal diagnosis varicella that were dual-coded increased substantially between 2009 and 2015 (p < 0.001; proportion <4% until 2009, 22.5%-28.8% from 2015 onwards), and with age (<15 years:<13%, ⩾65 years:>40%, from 2015 onwards). The proportion of hospital episodes with principal diagnosis zoster that were dual-coded also increased over time (p < 0.001), though was lower than observed in hospital episodes with principal diagnosis varicella. Hospital episodes with principal diagnosis post-herpetic neuralgia were rarely dual-coded.

After 2009, hospital episodes with principal diagnosis varicella, particularly in older age groups, frequently and increasingly have an additional zoster or postherpetic neuralgia code. Increased availability of real-time polymerase chain reaction testing and inadequate documentation in hospital medical records may have contributed to this.Implications for health information management practice:As hospitalisation data are extensively used to estimate disease burden and inform public health policy, the dual-coding issues identified require further investigation and mitigation.