Outbreak of scabies among preschool children, Accra, Ghana, 2017

The outbreak occurred in Presbyterian Secondary Staff Basic School in the La Nkwantanang Madina municipality of the Greater Accra Region. The total population of the school was 3674. The population of the preschool children was 845. The outbreak investigation was conducted from March 14 to May 17, 2017.

The following definitions were used:

A pupil or staff of the Presbyterian Secondary Staff Basic School with clinical signs and symptoms of scabies (rash, severe pruritus, burrows).

A line listing template was adopted from a scabies outbreak investigation report by the Department of Health, New Jersey, USA [17]. To find cases, physical examinations were conducted by a team of four GFELTP residents comprising: two physicians, one disease control officer, and a biologist. The team moved together from one class to the other and examined each pupil together – one performing the physical examination and the remaining observing closely. Based on the case definitions, at least, three of these four investigators had to agree on the clinical diagnosis of scabies for it to be added onto the line list. This approach was taken to improve inter and intra-operator reliability of examination findings.

Data of cases that were captured on the line list included: the name, age, class, place of residence, duration since onset, signs and symptoms (rash, burrows, itching, excoriation, crusting, presence of secondary bacterial infection) results of laboratory test, duration of treatment, and some risk factors (household size, number of baths per day, type of bedding, and hygiene practices).

We took two types of specimens: skin scrapings for the isolation of scabies mite, their eggs, or faeces; and wound swaps to identify agents responsible for secondary bacterial infection of scabies wounds.

First, we performed skin scrapings at the end of the burrows in non-excoriated and non-inflamed areas of scabies lesions unto filter papers using sterile scapel blades size# 15. We transferred scrapings from each site unto a microscopic slide, added 2 drops of 10% potassium hydroxide (KOH), mixed well, applied a cover slip, and ensured that no air bubbles were trapped within. We labeled these slides, placed them on cotton wool soaked in 10% KOH, transferred them into petri dishes, and then covered and sealed each with cello tape. We transported the petri dishes to the laboratory in a canister. Within seven hours of preparation, the biomedical scientist of our investigation team examined the slides under a light microscope for mites, their eggs, or faeces. Two other microbiologists cross examined the slides in turns. Negative samples were incubated for 72 for possible fungal growths.

We conducted an environmental assessment. This included an assessment of the state of classrooms, average class occupancy, seating arrangement, sleeping conditions during siesta, washroom hygiene, and the general state of cleanliness of the school premises.

We conducted descriptive and inferential statistical analyses. Results of univariate analysis of categorical variables were expressed as frequencies and proportions; and results for continuous variables were expressed as median and range. We described the data in terms of time, place and person. We constructed an epidemic curve to show the onset, and illustrate the magnitude and mode of propagation of the outbreak.

We calculated the following: overall attack rate (AR), and specific attack rates for age and sex. Attack Rate Ratios (ARR) and their corresponding 95% confidence intervals (CI) were estimated to determine the association of scabies with possible predictors (e.g. sex, class, age). Data entry and cleaning was done using Microsoft excel version 2010. We used Microsoft excel version 2010 for the descriptive analysis, and STATA version 13.1 for the inferential analysis.

This outbreak investigation was deemed a response to a public health emergency by the Ghana Health Service and hence did not require a formal review by Ethical Review Committees. Since all respondents were minors, a written consent was obtained from the Parents Teachers Association (PTA) of the school. All pupils who participated in the investigation accepted to be interviewed and examined without any form of coercion or inducement. The privacy of respondents during screening, and confidentiality of captured data were observed throughout the investigation. Data were kept under password and made available strictly on a need to know basis.

A total of 823 pupils were screened and all of them were preschool children (crèche to kindergarten 2). From these, 92 scabies cases were identified of whom 51.1% (47/92) were males. The median age of cases was 4 years (range 2–7 years), and the modal age was 3 years. The overall attack rate was 11.2% (92/823). There were no fatalities during the period of investigation.

The index case was a 3-year-old boy who was in the nursery one class. His mother is a community health nurse who noted that her son had developed pruritic rashes on the face and neck which did not respond to topical antibiotics for a period of one week. In the evening of March 14, 2017, she suspected scabies and placed a personal call to a GFELTP resident who is a medical officer to consult on her son’s condition. The next morning, the resident made a visit to the school, confirmed the diagnosis, and identified more cases in the pupil’s class. Affected pupils presented with typical pruritic lesions of scabies with excoriations from repeated scratching. Cases presented with typical signs and symptoms of scabies (Fig. 1). The worst affected body part was the face (Fig. 2). Some of the lesions had developed suppurative secondary bacterial infections. Nearly 10% of cases had pyoderma from secondary bacterial infections.

The epidemic curve showed a propagated source for the outbreak (Fig. 3). The earliest case captured in the investigation (a likely primary case) occurred in the epidemiological week 49 of 2016. The index case developed the scabies in the epidemiological week 7 of 2017. The number of cases rose gradually from epidemiological week 1 of 2017 until epidemiological week 7 when the numbers rose sharply; peaking in epidemiological week 9. The last case occurred in epidemiological week 18 of 2017.

The sex specific attack rate was 11.5% for males, and 10.8% for females (Table 1). However, the risk of attack did not differ by sex (ARR: 0.93; CI: 0.67–1.28). Compared with the 2-year-old pupils, the 3-year-old pupils were more likely to develop scabies (ARR: 4.77; CI: 3.18–6.98). Using the least affected class (crèche) as the reference class, the worst affected class was the nursery 1(ARR: 5.14; CI: 3.44–7.50).

The school compound was walled. The immediate grounds to the classrooms were paved with concrete blocks. In the crèche and nursery classes, pupils shared sleeping mats during siesta. Each class from the nursery level and higher, was subdivided into four; each with an average of about 45 pupils. Each class had running water from a Veronica bucket for routine hand washing. The school compound and classrooms were clean. The school had washrooms with running water. However, water supply was not constant, and the facilities were under pressure from the large population of pupils.

In our study, nearly 10% of the cases presented with pyoderma. The intense pruritus typical of scabies is caused by a hypersensitive reaction to components of the saliva, eggs, and faecal material of the scabies mites. Repeated scratching results in excoriation of the epidermis. These excoriations serve as entry points for both skin commensals and pathogenic bacteria. Pyoderma is therefore a common complication especially among scabies patients in the tropics who have multiple lesions [24]. In 1997, a study of the prevalence of secondary infections among scabies patients in Ghana revealed that, of 110 patients who developed secondary infections, culture results showed a mixture of both aerobic and anaerobic bacteria. Staphylococcus aureus was the most isolated aerobic bacteria species (39.1%), and Pepostreptococcus spp. was the most isolated anaerobic bacteria species (14.2%) [25]. Similarly, in our study, Staphylococcus aureus and streptococcus spp. were identified as the main agents causing secondary bacterial infection among pupils with suppurative scabies sores. If streptococcal skin infections are not effectively treated, APSGN can result. In Trinidad, the number of nephritogenic strains of streptococci isolated increased with a rise in the occurrence of scabies and APSGN in the general population [12, 25]. Lawrence and colleagues showed that, the control of scabies and the associated streptococcal infection of scabies sores among children significantly reduces haematuria [26]. We infer that, the significant reduction of haematuria in their study resulted from the reduction in renal damage usually caused by APSGN – a complication of streptococcal infection of the scabies sores. Outbreaks of APSGN coincide with those of scabies, and asymptomatic renal disease is also common [27, 28]. These insults to the kidney in childhood; as in the case of these 92 preschool children, contribute to the development of chronic kidney disease and subsequent renal failure in adulthood [27, 29].

The laboratory diagnosis of scabies requires the microscopic detection of the mite, ova, or faecal pellets. However, in our study, all the skin scrapings examined with light microscopy turned out negative for mite, their eggs, or faeces. This method is very specific, and a mite or eggs seen under the microscope are diagnostic. We diagnosed cases using typical clinical signs and symptoms. In resource limited settings like Ghana, clinical diagnosis is the more practical way of diagnosing scabies because the sensitivity of skin scrapings is so low that its diagnostic usefulness is questionable [4]. In their study of the comparison of dermoscopy, skin scraping, and the adhesive tape test for the diagnosis of scabies in a resource-poor setting in northeast Brazil, Walter and his colleagues found that the sensitivity of skin scraping was low (0.46; 95% CI, 0.31–0.62) and concluded this method cannot be recommended as a diagnostic tool in such setting [30]. In the light of these challenges, a practical approach for the diagnosis of scabies that includes the presence of papules, vesicles, pustules, itching (especially at night), and a positive family history as proposed by Heukelbach and colleagues is an acceptable method for the diagnosis of a case [21, 31]. These evidence based practicalities informed the clinical approach we used for case identification in our investigation of the outbreak. Epiluminescence microscopy and high-resolution videodermatoscopy seem to be promising diagnostic methods [32, 33]. Even then, there have been no robust studies to compare the sensitivity and specificity of clinical diagnosis and microscopic examinations of the skin. The high equipment cost means that, the techniques are accessible only in well-resourced settings. Thus, the diagnosis of scabies and hence, the detection of outbreaks would remain largely clinical in Ghana for the time being.

Given the ages of the affected pupils, they were unable provide detailed clinical history of their condition. Many parents were hard to reach; both at home (via home-visits) and by telephone calls, to assist with details of the disease progression. We were also unable to carry out contact tracing in the communities within which affected pupils resided.

We carried out mass treatment of pupils for scabies using benzyl benzoate cream. We referred pupils with scabies sores to the municipal hospital for further management. We conducted health education on scabies for staff and pupils of the school. As part of the continual health education, we posted pictures showing the clinical presentations of scabies on all school notice boards to raise awareness and help improve surveillance of scabies within the school. We supervised the cleaning and disinfection of classrooms, sleeping mats, and washrooms. School authorities welcomed our recommendation to stop the practice where pupils share sleeping mats at school.