Scabies in 604 Patients: A Glimpse into the Disease Burden and Its Associated Mortality in Hong Kong

Scabies is a worldwide parasitic dermatosis with a significant health burden on the young and the elderly. Statistics about the prevalence of scabies in Hong Kong are not available. This is a retrospective study of patients from a regional hospital cluster in Hong Kong with microscopy-documented Sarcoptes scabiei infestations from January 2018 to December 2022. The condition was categorised into classical scabies and crusted scabies upon clinical presentation. Demographic data, comorbid diseases, mobility and residential status, seasonal variability, secondary bacterial infection, treatment and outcomes were described. These were compared between classic and crusted scabies. In total, 604 patients were identified, representing 51.65 per 100,000 discharged patients during the study period. The median age was 84 years and 54.5% were male. The majority (506 or 83.8%) came from residential care homes for the elderly. The mean time from admission to diagnosis was 8.8 days for community-acquired infestation. There were 564 and 40 cases of classic and crusted scabies, respectively. The two groups of patients were comparable in terms of residence in elderly homes, co-existing chronic illnesses, mobility, and time from admission to diagnosis. Forty-five (7.5%) patients had positive blood cultures temporally associated with scabies. Patients with crusted scabies were at higher risk for bacteraemia (7/40 versus 38/564, p = 0.022). Permethrin and benzyl benzoate were the most popular treatment regimens, with treatment failure observed in 59/397 (14.4%) and 18/173 (10.4%), respectively. There were 172 (28.5%) mortalities within 30 days of scabies diagnosis. Thus, the burden of scabies infestation is significant in Hong Kong. Hospitalised patients diagnosed with scabies are mainly senior citizens living in residential care homes for the elderly, suggesting reservoirs of S. scabiei in the community. Of concern, bacteraemic illnesses are common and significant mortality is temporarily associated with infestation. With a rising elderly population, there is a pressing need to understand and control scabies in Hong Kong. Our study did not find that common medical illness, besides immunosuppressive therapy, predisposed patients to crusted scabies. The crusted form of scabies was associated with a higher risk of bacteraemia. The current study provides a better perspective of the disease load of scabies in Hong Kong.