Paediatrics (RCH) - Theses
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ItemIvermectin-based mass drug administration for the serious bacterial complications of scabies( 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.
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ItemImproving the diagnosis of scabies in low-resource settings( 2020)Scabies is a parasitic disease and a global health problem that predominantly affects disadvantaged communities in low-resource settings. Scabies significantly impacts the health and quality of life of those with the disease. To accurately assess the global burden of disease and to compare data across regions, standardised diagnosis with consistent disease definitions is necessary. In low-resource settings, diagnosis by clinical assessment is the principal diagnostic method. In the absence of available experts, non-expert health workers are likely to play critical roles in diagnosis, including for prevalence mapping. Currently, standardised processes for clinical diagnosis for scabies do not exist. This thesis explores the diagnosis of scabies in low-resource settings and the role and utility of non-expert health workers in the diagnosis of scabies. Chapter 3 describes the evaluation of non-expert health workers in the diagnosis of scabies and impetigo using clinical criteria. The diagnosis of four briefly-trained nurses was compared to the consensus diagnosis of two experienced doctors. The sensitivity of the nurses’ diagnosis compared to the reference standard was 55.3% for scabies with a specificity of 89.9% Sensitivity for moderate to severe scabies was 93.5% with a specificity of 74%. The accuracy of diagnosis by non-expert health workers is promising and may be acceptable for scabies and impetigo disease mapping in low-resource settings. Chapter 4 describes the development and evaluation of a training protocol for the diagnosis of scabies and impetigo for non-expert health workers. The aim of this study was to measure the change in knowledge and confidence of the participants and explore their experience and perceptions of the training. Training was evaluated using a case-based test, a questionnaire and semi-structured interviews. The overall results of the case-based test were 90% for scabies and 75.5% for impetigo. The mean score for both self-reported knowledge and confidence increased from 2.5 to 4.5 following training and scores increased for all nurses (mean difference 2, 95%CI 1.1-2.9, P=0.005). The study showed that training local health staff in scabies diagnosis was enjoyable for participants and led to improvements in self-reported knowledge and confidence. Chapter 5 investigates the prevalence of scabies and impetigo using a cross-sectional study in a primary school in Gizo in the Solomon Islands. Using the International Alliance for the Control of Scabies (IACS) diagnostic criteria the classified the diagnosis of scabies. The prevalence of scabies was 54.3% and prevalence of impetigo was 32.1%. 63.5% of those with impetigo had scabies, corresponding to a population attributable risk of 11.8%. The study highlighted the extremely high burden of these diseases supporting the need for interventions for scabies in this community. Chapter 6 evaluates the methods of data collection, analysis and display for describing in detail the distribution of scabies lesions in a pilot study. The study used a novel technique of representation of dermatological lesions in the form of a choropleth map. The study found that the methods used were feasible for a larger population and would describe valuable detailed information on specific lesion location in scabies. The study will provide information on lesions at specific body sites to determine if simplified examinations are appropriate for prevalence surveys. The public health control of scabies requires identification of high-prevalence communities to target interventions, as well as methods to monitor the effectiveness of interventions. Such programs would be dependent on accurate and standardised diagnosis for population mapping. This thesis suggests methods to improve the diagnosis of scabies in low-resource settings. Modifications to training and diagnostic methods are likely to improve diagnostic accuracy. Improvements to scabies diagnosis will contribute to efficient collection methods and reliability of prevalence data.