Scabies is an intensely pruritic, highly contagious skin infestation caused by the arachnid mite Sarcoptes scabiei variant hominus. Scabies was added to the World Health Organization’s list of neglected tropical diseases (http://www.who.int/neglected_diseases/diseases/scabies/en/) in November 2013 because it accounts for a substantial proportion of skin disease among low-income countries, and despite the substantial burden of disease, it has been largely absent from the global health agenda [1,2]. The addition of scabies to this list increases publicity for this largely ignored disease and recognizes that new programs are needed to control scabies and its sequelae [1,2]. The highest rates of scabies are reported among children from low-income countries where the prevalence typically ranges from 0.2% to 24%; however, it is endemic among tropical regions, with prevalence ranging from 10% to 25%, and areas in the Pacific region have reported prevalence as high as 50% [1,3–11]. Although the incidence of scabies has not been determined previously in American Samoa, a 2009 study of 8,767 children in western Samoa reported a prevalence of 4.3%, whereas a prospective study in Fiji reported a prevalence of 18% among school children (aged 5–15 years) and 14% among infants [9,10].

Scabies transmission occurs through direct and prolonged contact, and possibly through sharing contaminated clothing or bedding. Infestation causes intense pruritus, particularly at night, often causing sleep disruption. Excoriation of lesions can lead to secondary bacterial superinfections [4,12,13], therefore treating an infestation early during the disease process may prevent bacterial superinfection and scabies transmission to close contacts, and treating scabies in a community leads to a concurrent reduction in rates or pyoderma [10,14]. The most common causes of bacterial skin and superinfection among low-income nations are group A Streptococcus (GAS) and Staphylococcus aureus [3,9,14–16]. GAS skin infections can lead to poststreptococcal glomerulonephritis, and certain epidemiologists hypothesize that acute rheumatic fever might also be a sequela [6,9,14,17]. Reinfestations can be prevented by properly applied permethrin cream (5%), or other effective scabicidal treatment, administered to all close contacts in addition to the patient and environmental remediation, including washing contaminated bedding and clothing in hot water [1,4,12,13,18]. In addition to sleep disturbance, consequences of scabies include loss of school or work, economic burden on families or persons, and secondary bacterial superinfection [4,9,12,13]. Risk factors for scabies among low-income countries include young age, illiteracy, low socioeconomic status, shared clothing and beds, and household overcrowding [4,6–8,11,19,20].

Scabies among American Samoan (AS) children is perceived to be a substantial problem by the local medical community, with certain patients reportedly presenting for care multiple times because of persistent infestation, reinfestation, and bacterial superinfection. The incidence of scabies had not been described in AS; a fuller understanding of the burden of scabies is imperative for developing targeted community interventions. We conducted a retrospective study to describe the estimated incidence of scabies infestation and the prevalence of reinfestation and bacterial superinfection of scabies lesions among infants and children aged ≤14 years in AS; we achieved these goals and made recommendations to control the epidemic on the basis of our report.

Pharmacy record review identified 1,733 children aged ≤14 years with a prescription for permethrin cream (5%) during 2011–2012; 1,139 of these children had a diagnosis of scabies in their medical record. Among the AS population of 19,425 children aged ≤14 years, we identified 613 children with scabies during 2011 and 526 during 2012. The annual average was 570 cases, or 29.3 cases/1,000 children. Estimated incidence was highest among children aged 0–4 years and declined with advancing age; children aged <1 year had the highest incidence (99.9/1,000 children), and children aged 14 years had the lowest incidence (7.3/1,000 children) (Table 1). Compared to children aged 10–14 years, children aged 0–4 years were 4.9 times more likely to have been diagnosed with scabies, and children aged 5–9 years were 2.2 times more likely to have been diagnosed with scabies (Table 2).

Incidence also varied by county; children who reside in each county on Tutuila Island besides Sa’ole were significantly more likely to have scabies than those living in Sa’ole County (incidence ratio range 1.8–3.2) (Table 2 and Fig 1). None of the variables tested were substantial effect modifiers or confounders.

Bacterial superinfection was present at the time of scabies diagnosis among 604/1,139 (53.0%) children (Table 1). Among 613 children with scabies during 2011, 94 (15.3%) had one or more reinfestation; 64 (68.1%) of these were superinfected at the time of the second scabies diagnosis. Antibiotics prescribed included cephalexin, amoxicillin, penicillin, azithromycin, and trimethoprim-sulfmethoxazole. The median time between the first and second diagnosis was 86 days (range 14–341 days). Scabies incidence did not vary consistently by month of diagnosis (Fig 2).

Our study demonstrates that scabies and associated bacterial superinfections cause substantial morbidity among AS children. During 2011–2012, an average of 29.3/1,000 children and approximately 1 of 10 infants received a scabies diagnosis each year. Scabies incidence decreased with increasing age, which is consistent with previous studies [1,13]. This likely results from younger children being in close contact with multiple family members and often being held, which provides opportunities for exposure to infected family members. The predominance among males contrasts with previous studies; additional research is needed to understand the reasons for this difference [4]. Scabies does not appear to follow a seasonal pattern, which is expected in tropical regions where weather patterns are consistent throughout the year [4,9,23–25].

The difference between the number of children with a permethrin prescription (1,733) and the number of children with a scabies diagnosis (1,139) can be explained by prescribing practices; every household member receives a prescription when a child is diagnosed with scabies, hence many of these children may have been siblings that did not seek medical care.

To understand the variation of scabies incidence by county, we reviewed distances between the pharmacy and outpatient clinics. The pharmacy is located centrally on the island in Maoputasi County, which has among the higher incidences of scabies. However, outpatient clinics are located in counties with both higher and lower incidences (Fig 1), which indicates that distance from outpatient clinics does not influence scabies incidence. In addition, approximately 93% of the population resides in urban areas, indicating that differences between urban and rural lifestyles have limited effect on county differences in scabies incidence [22]. The possibility exists that lifestyle differs by community or that scabies is easily maintained after established locally.

The high frequency of reinfestation and the limited time between recurrent infections indicate that these subsequent infections are likely because of incorrectly applied treatment, treatment failure, or inadequate treatment of the environment or close contacts. This might allow scabies to persist in the child’s environment and among close contacts after being established [26,27].

The high frequency of bacterial superinfection might result from crowded housing and inadequate hygiene [1]. Delays in seeking care also allow time for the secondary lesions to develop in the broken skin. The prevalence of both impetigo and scabies is higher in the South Pacific region than among a majority of low-income nations, and scabies has been identified as a risk factor for bacterial skin infections. For example, in Fiji, children with scabies were 2.4 times more likely to have impetigo than children without scabies [4,6,9,10,28]. Additionally, intervention studies designed to treat scabies have reported a substantial reduction in pyoderma even without use of antibiotics or other pyoderma-specific interventions [16,29–31]. Bacterial superinfection can lead to serious sequelae, including cellulitis and abscesses. Among more severe cases, bacteremia and sepsis can occur [14].

Our study has likely underestimated the incidence of scabies among AS children because we only included children who sought medical care at LBJTMC or one of the outpatient clinics and filled a prescription of permethrin, and we might have missed cases among persons not seeking treatment by using traditional or over-the-counter medicine obtained outside the medical system, not filling prescriptions because of expense or pharmacy inaccessibility, or obtaining medication from a friend or family member. All household contacts are prescribed permethrin when scabies is diagnosed, yet only those children who were treated by a doctor and had received a scabies diagnosis were included in this analysis. However, since scabies is diagnosed clinically in AS, it is possible some initial scabies diagnoses and reinfestations were actually misdiagnosed since scabies can mimic many common skin diseases in the tropics. Another limitation is our use of a broad definition of bacterial superinfection, potentially inflating this estimate; cases of unrelated bacterial infection might be included if not clearly documented in the record.

Although scabies is known to be particularly prevalent throughout the Pacific region, medical personnel report socioeconomic and lifestyle concerns that are particular to AS and might contribute to the problem. Traditional medicine is commonly the first choice for care; families often do not seek care at the hospital or outpatient clinic until an infestation, or secondary infection, is severe, allowing time for scabies to spread to other family members. Living conditions are often crowded, with certain families sharing a living space, beds, and clothing. Because permethrin prescriptions cost $10/patient, treating a multiple family members might not be feasible for multiple families. Finally, AS families often do not have access to hot water to wash clothing, and do not have enough bedding and clothing to bag everything for seven days to kill the mites. This can allow scabies mites to survive in the environment, infesting family members, and leading to reinfestations. (Personal communication with Lucy Goh and James Marrone.)

Our study describes the previously unknown incidence of scabies among AS children and indicates that age and county are associated with scabies incidence. Additional community-based studies are needed to examine additional risk factors for scabies. Such studies might include cross-sectional and prospective studies of children in school or other community venues. This might allow a more accurate assessment of the incidence of scabies, regardless of whether the children present for medical care. Parent or child interviews might help elucidate risk factors for and knowledge and attitudes about scabies. Understanding county differences in lifestyle, knowledge, attitude, and behavior concerning scabies might support recommendations for scabies control and help target interventions to areas with higher incidence.

On the basis of the success of previous education efforts in different community settings, we recommended education for medical providers about scabies diagnosis and creation of recommended protocols for scabies treatment and environmental control [1,9,11]. Existing algorithms used to diagnose common childhood skin conditions are available, which can be useful for training providers [32]. We propose that interventions should focus on families with young children and on those families residing in counties with the highest incidence. Education about the importance of early treatment to prevent secondary infection and treatment of all close contacts and the environment to prevent reinfestation and transmission should be emphasized. Mass drug administration campaigns, by using either permethrin cream (5%) or oral ivermectin, have led to temporary decreases in the incidence of scabies among certain countries and might be considered for AS. However, these interventions are costly and often impractical, given the limited resources. Timely diagnosis, treatment, increased awareness and case finding, and education for health care workers, patients, and the community are the mainstays of scabies prevention [1,4,9,11,12,29–31].