Arua District is located in Northwestern Uganda and is bordered by the Democratic Republic of the Congo (DRC) to the west. The district has a total population of about 782,000 persons .The main economic activities in Arua district include cross-border trade with South Sudan and DRC, agriculture, and livestock farming, characterized by significant movement of livestock into and out of the district. Arua District has 18 sub-counties. Rhino Camp sub-county is one of the sub-counties occupied by both refugees (mostly from DRC) and Ugandan nationals and is named for its proximity to a Ugandan national park which contained white rhinos.
Case definition and case-finding
We defined a suspected cutaneous anthrax case as onset of skin lesions (e.g., papule, vesicle, or eschar) in a person residing in Rhino Camp sub-county, Arua District from 25 December2017 to 31 May 2018. We defined a confirmed anthrax case as a suspected case with PCR-positivity for Bacillus anthracis from a clinical sample (swab from skin lesions/vesicles, or blood samples).
To identify cases, we reviewed medical records at Rhino Camp Health Centre III We also conducted additional case searches in the affected community with support from Community Health Workers. We developed a line list of cutaneous anthrax case-persons with patient age, sex, residence, date of onset of signs and symptoms, laboratory investigations, specimens collected, and coordinates of the case-persons’ households.
We performed descriptive epidemiology on the line-listed case-persons. Using an epidemic curve, we described the case-persons by time of onset. Using population data obtained from the district population office, we computed attack rates by age-group, sex, and parish. We also drew a choropleth map using QGIS software version to describe case-persons by parish.
We interviewed 14 suspected case-persons. The key exposures that we explored were those that occurred from 25 December 2017 onwards, including carrying a dead animal to a slaughter site, skinning of a dead animal, dissecting a dead animal, carrying already-dissected parts of dead animals, preparation and cooking of meat of dead animals, contact with hides through skinning and preparation and having contact with soil through digging.
Retrospective cohort study
To identify specific animal-related exposures that increased risk for cutaneous anthrax among humans, we formed a cohort among all members of households in which at least one person had contact with the carcass of or products from any animal suspected to have died of anthrax.
We collected 9 skins lesion swabs from patients with cutaneous anthrax and shipped the samples to the Uganda Virus Research Institute (UVRI; Entebbe, Uganda) for testing. The skin lesion swabs and blood specimens were tested at UVRI using rPCR following standard protocol. 
In addition to collecting and testing swabs and blood samples from case-persons, we also tested hides from three implicated cows (hides from cows reported to have died suddenly) using an InBios Active Anthrax DetectTM (AAD) (Anthrax Rapid Test lateral flow immunoassay). The AAD is a point‐of‐care assay that is under investigational use for detecting Bacillus anthracis capsular polypeptide (polyglutamic acid) in suspect animal cases . AAD was developed as a point of care test for presumptive human inhalation of Anthrax spores . We sample the sample in 600µL of sterile phosphate buffered saline, vortexed for 10 s, and, after pipetting the solution multiple times, applied 10 µL to the AAD cassette. Specimen from the dried hide were shipped to the US Centers for Disease Control and Prevention (CDC; Atlanta, GA, USA) for confirmatory testing. DNA extraction on the specimen was performed using a QIAGEN Blood Mini Kit . The resulting DNA was tested using real-time reverse transcription PCR for B. anthracis from the Laboratory Reference Network. A formalin-fixed sample from the dried hide was routinely processed, embedded in paraffin, and stained with hematoxylin and eosin, Lillie-Twort gram stain, and Warthin-Starry silver stain. Immunohistochemistry assays using mouse monoclonal antibodies targeting the B. anthracis cell wall and capsule were performed by using an immunoalkaline phosphatase polymer system as previously described [15, 16]
We observed the possible sites of animal infection, including grazing land and kraals. We mapped out all the kraals in Ombeniya village, identified communal grazing points, and observed both kraals and grazing points for evidence of remains of dead animals. We evaluated the carcass disposal methods on the grazing land. We also observed for the presence of human digging activities at points where sudden animal deaths had occurred.
We used Epi-info Version 7 for data analysis. Descriptive analysis was conducted by person, place and time and results were summarized using attack rates, an epidemic curve, and maps. To measure the associations between exposure variables and illness status, we estimated risk ratios (RR) and their 95% confidence intervals.
Approval to conduct this investigation was sought from the Ministry of Health of Uganda through the office of the Director General Health Services. The Division of Global Health Protection, Centers for Disease Control and Prevention determined that this investigation was not human subjects’ research. Verbal consent was obtained from case-persons and other household members 18 years or older. For participants <18 years, we sought verbal assent after consent from their parents or guardians. We also sought permission from the local authorities to undertake you’re the outbreak response. Privacy was guaranteed by conducting interviews in a secure place where none of the people around the home could follow the interview. The questionnaires were kept under lock and key to prevent disclosure of personal information of the respondents to individuals who were not part of the investigation.