Paediatrics (RCH) - Theses

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Start date: 2020 × End date: 2022 × Subject: Public health × Author: Thean, Li Jun ×

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    Ivermectin-based mass drug administration for the serious bacterial complications of scabies
    Thean, Li Jun ( 2022)
    Scabies is a skin disease caused by the mite Sarcoptes scabiei var. hominis, which is especially prevalent in populations experiencing overcrowding and poverty. Recognised as a neglected tropical disease by the World Health Organization in 2017, scabies is characterised through skin lesions and intense itch. The host is made vulnerable to secondary bacterial infection through skin breaches, scratching and inhibition of the complement system via mite secretions. Bacterial infection predominantly caused by Staphylococcus aureus and/or Group A Streptococcus most commonly manifesting as impetigo can complicate scabies. Impetigo can progress to more complicated skin and soft tissue infection, invasive bacterial infection and post streptococcal sequelae which cause significant morbidity and mortality. Previous studies in the Pacific Islands, including in Fiji, demonstrated that ivermectin-based mass drug administration substantially reduces scabies prevalence by approximately 90%, and leads to a concomitant reduction in impetigo prevalence by 60% to 70%. The focus of this thesis was to determine if ivermectin-based mass drug administration also leads to a reduction in the more serious bacterial complications of scabies. The studies and intervention described in this thesis take place in Fiji’s Northern Division (population ~131,914 in 2017). Four studies are reported in the thesis. The first study investigated the burden of hospitalisations for skin and soft tissue infections using prospective surveillance at the referral hospital of the Northern Division, and found a very high population incidence of 647 admissions per 100,000 person-years (95% CI 571-660). The second study investigated the burden of invasive infections caused by S. aureus and group A Streptococcus, using prospective surveillance also at the referral hospital, and found a high incidence at 45.2 and 12.3 per 100,000 person-years, respectively. The third study investigated the incidence of primary healthcare presentations for scabies and skin and soft tissue infections using a prospective surveillance system established at all primary healthcare facilities in the Northern Division, and found that there were 13,736 presentations over 50 weeks, equivalent to a population incidence of 108 presentations per 1000 person-years. The final major study investigated the impact of ivermectin-based mass drug administration on the bacterial complications of scabies. Ivermectin-based mass drug administration was deployed across the whole of the Northern Division. Coverage of mass drug administration was high – with the first dose achieving 97% and the second dose 87% coverage. The primary outcome measure was the annual incidence of hospitalisations for skin and soft tissue infections, with the study finding that the incidence declined significantly by 17% in the year after mass drug administration (from 467 to 388 per 100,000, incidence rate ratio 0.83 95% confidence intervals 0.74% to 0.94%). This finding was supported by a reduction in the annual incidence of primary healthcare presentations by 21%, and by a reduction in scabies and impetigo prevalence by 29% and 60% respectively. There was no decrease in the incidence of invasive infections and post streptococcal sequelae. Overall, this thesis demonstrates that scabies control through mass drug administration can lead to a reduction in the incidence of bacterial skin and soft tissue infections, measured as a fall in healthcare utilisation and community prevalence. These results are encouraging and provide further evidence of the broader benefits of scabies control via mass drug administration. In settings where scabies is endemic and where resources are limited and health priorities compete, this thesis highlights the underestimated burden of scabies and strengthens the case for policy targeting control of this neglected tropical disease.