Treatment failure is considered as an important factor for the increase in scabies incidence over the last decade. However, the regional and temporal differences as well as predictors of therapy failure are unclear.
A systematic review of the prevalence of treatment failure in scabies patients and investigation of associated factors.
We searched MEDLINE, EMBASE, CINAHL, Web of Science, Scopus, Global Health and the Cochrane Central from inception to August 2021 for randomized and quasi-randomized trials, as well as observational studies that enrolled children or adults diagnosed with confirmed or clinical scabies treated with permethrin, ivermectin, crotamiton, benzyl benzoate, malathion, sulfur, or lindane, and measured treatment failure or factors associated with treatment failure. We performed random-effects meta-analysis for all outcomes reported by at least two studies.
147 studies were eligible. Overall prevalence of treatment failure was 15.2% (95% CI: 12.9 to 17.6; I2=95.3%, moderate certainty evidence) with regional differences between WHO Regions (P=0.003) being highest in the Western Pacific Region (26.9% [95% CI: 14.5 to 41.2]). Oral ivermectin (11.8% [95% CI: 8.4 to 15.4]), topical ivermectin (9.3% [95% CI: 5.1 to 14.3]) and permethrin (10.8% [95% CI: 7.5 to 14.5]) had relatively lower failure prevalence compared to the overall prevalence. Failure prevalence was lower in patients treated with two doses of oral ivermectin (7.1% [95% CI: 3.1 to 12.3]) compared to those treated with one dose (15.2% [95% CI: 10.8 to 20.2]; P=0.021). Overall and permethrin treatment failure prevalence in the included studies (1983-2021) increased by 0.27% and 0.58% per year, respectively. Only three studies conducted a multivariable risk factor analysis, none assessed resistance.
A second dose of ivermectin showed lower failure prevalence than single dose ivermectin which should be considered in all guidelines. Increasing treatment failure over time hints toward decreasing mite susceptibility against several drugs but reasons for failure are rarely assessed. Ideally, scabicide susceptibility testing should be implemented in future studies.