Prevalence of scabies and impetigo in the Solomon Islands: a school survey

This was a cross-sectional, school-based study that took place in the public primary school in the town of Gizo, the capital of the Western Province of the Solomon Islands. The population in the Gizo region is approximately 7000 [11]. The setting was selected because it is the site of a planned trial. The school was selected as the study site because of the simple facilitation of recruitment of participants within a school setting and its convenient location within the centre of the town.

At the commencement of 2018, the primary school had a school roll of 682 students, consisting of students residing in Gizo town and those who travel by truck or boat from surrounding villages or islands. Students at the primary school are aged 4 to 15 years, with class groupings based on aptitude rather than age.

All students attending Gizo Primary School were eligible for inclusion in the study. All patients underwent a standardized examination for scabies and impetigo.

Clinical assessment was performed by doctors with expertise in scabies diagnosis, and by nurses with clinical experience in scabies diagnosis, supplemented by a training program on the diagnosis of scabies, impetigo and other locally common skin conditions. Scabies was diagnosed using the 2018 IACS Criteria [7]. Although eight subcategories exist in the IACS Criteria, only four were relevant for diagnosis in this study (Table 1). Subcategories of diagnosis that required specialized equipment (including microscopy and dermoscopy) or required examination of the genitals, were not used, as these were not practical for a field survey in this context. Impetigo was diagnosed on the presence of papules, pustules or ulcerative lesions with associated erythema, crusting or pus. Skin examination consisted of assessment of exposed areas: the feet and legs to the thighs, hands to the upper arms, neck, face and scalp. Students were in school uniform which consisted of above-knee shorts and above-elbow shirts or dresses. Shoes were removed prior to examination. A focused history of standardized questions was taken of all participants with skin lesions consisting of information required for the IACS Criteria classification. Questions included whether participants experienced itch. Contact history was assessed by asking if participants lived with someone, or had a friend or classmate with itch, or if they lived with someone, or had a friend or classmate with a rash that looks like scabies. Participants were shown images of people with typical scabies rashes to assist these questions. History was taken in the local language (Solomon Islands Pijin). Permethrin was supplied for individuals diagnosed with scabies. Permethrin was also supplied for household contacts of diagnosed children, as per local treatment protocol. No treatment was supplied to examined children without scabies. If other conditions were diagnosed, referral was provided to the local health clinic.

Demographic information was collected including participant age, sex and school grade.

Scabies diagnosis was classified into one of three IACS Criteria subcategories (Table 1).

Following methods used in previous studies, severity of scabies and impetigo was assessed based on the number of lesions present [12, 13]. Scabies was categorized as: mild, 1 to 10 lesions; moderate, 11 to 49 lesions; or severe, 50 or more lesions. Impetigo was classified as: very mild, 1 to 5 lesions; mild, 6 to 10 lesions; moderate, 11 to 49 lesions; or severe, 50 or more lesions.

Prevalence for scabies and impetigo was calculated for each demographic group. Risk ratios were calculated using generalized linear models, adjusting for age group and sex. Population attributable risk was calculated to further analyze association between scabies and impetigo [14].

Data were collected on forms during the study period and then transcribed and uploaded to a REDCap study database (Research Electronic Data Capture), hosted at Murdoch Children’s Research Institute [15]. All statistical analysis was performed using Stata (version 15, StataCorp, College Station, TX, USA).

Parents were provided with written information regarding the study. A community information night was also held at the school where members of the study team provided further information and answered questions. Written consent was obtained from parents or guardians of all participants and verbal assent from children where possible.

Ethical approval was granted by the Royal Children’s Hospital Melbourne Human Research Ethics Committee (reference number 38099A) and the Solomon Islands Health Research and Ethics Review Board (reference number 05/18).

Overall, 176 participants had scabies (prevalence 54.3, 95% confidence interval [CI] 48.7–59.8), and 104 participants had impetigo (prevalence 32.1, 95% CI 27.0–37.5). Most scabies cases were mild (68.8%, n = 121) but 14 participants (8%) had severe scabies (Table 3). The majority of those with impetigo had very mild disease (n = 86, 82.7%, Table 3). The prevalence of scabies diagnosed by doctor and nurse examiners was similar (52.2, 95% CI 45.8–58.6; vs 61.0, 95% CI 49.2–72.0%).

Itch was reported in 81.8% of individuals with scabies (n = 144) and in 18.4% of those without scabies (n = 21, missing = 34). A positive contact history was reported in 92.1% (n = 161) of those with scabies, and in 52.6% of those without scabies who were asked (n = 60, missing = 34). The most common contact history reported was having a friend or classmate with a rash that looks like scabies (75, 95%CI 67.9–81.2, Table 4). Of those with scabies, 26.1% (n = 46) reported either a history of itch or a positive contact history and 73.9% (n = 130) had both history features. Of those without scabies, 46.5% (n = 53) reported either a history of itch or a positive contact history and 12.3% (n = 14) had both features.

The majority of scabies cases (n = 128, 72.7%) were classified as Clinical Scabies, subcategory B3, with typical clinical features, itch and contact history according to the IACS Criteria (Table 3). Only four individuals (2.3%) were identified to have clinically visible burrows (B1).

Scabies was more common in males than females (63.5% vs 45.8%, adjusted risk ratio [ARR] 1.4, 95% CI 1.1–1.7; Table 2) and the most commonly affected age group was children aged 10–12 years (61.4%; ARR 1.8, 95% CI 1.1–2.9, compared to age group 4–6 years; Fig. 1). Prevalence of impetigo was higher in males (41.7% vs 23.2%, ARR 1.7, 95% CI 1.2–2.4) but similar across age groups.

Participants with scabies had a higher prevalence of impetigo than those without scabies (66 of 176, 37.5% vs 38 of 110, 25.7%, ARR 1.5, 95% CI 1.1–2). Overall, 63.5% of those with impetigo had scabies, corresponding to a population attributable risk of 11.8% (95%CI 1.7–21.7, P = 0.02). Of the 18 individuals with greater than very mild impetigo, 14 (77.8%) had scabies, and of the individuals with moderate to severe impetigo, all had scabies (n = 6, 100%).