In this case, the blood culture was taken from an 8-year-old boy from rural Mpumalanga, South Africa who was admitted to the Steve Biko Academic Hospital on 23 September 2016 and was being investigated for a bladder mass and a 2-year history of enuresis (Figure 1). For this case isolate, the chocolate plate had pure growth of fine grey colonies after 14 h of incubation. This isolate was sent for Vitek 2 for identification and was identified as B. melitensis. Once this identification was noted, all further processing was done in a biological safety cabinet class 2 using Biosafety Level 3 precautions, as recommended by the United States Centers for Disease Control and Prevention. A Gram stain from the culture plates revealed Gram-negative coccobacilli which were catalase and oxidase positive and indole negative which was in keeping with a preliminary identification of Brucella species. The positive B. melitensis culture was sent to the National Institute of Communicable Diseases in Sandringham, South Africa on 24 September 2016, where the identification of the organism was confirmed using matrix-assisted laser desorption/ionisation time of flight (MALDI-TOF) mass spectrometry. The instrument used in this case was the Vitek MS (bioMerieux, Marcy-l'Etoile, France), Instrument software version 1.5.0.4, MYLA version 4.5.1, Knowledge Base (Database) version 3.2 (bioMerieux, Marcy-l'Etoile, France).
The blood culture was taken as part of 'routine' investigations as the child had no symptoms or clinical signs which may have led one to consider brucellosis as a possible differential diagnosis. The child was discharged once the blood samples were obtained. The outbreak response unit of the National Institute of Communicable Diseases was alerted to the case on 25 September 2016 and began further investigations and follow-up of affected individuals and possible contacts. It was discovered that the child's family had been consuming unpasteurised cow's milk from a local farmer for many years. This farmer's cattle were tested in late October/early November 2016 using standard South African veterinary testing guidelines. Sixty-eight cows were tested and 13 were found to be positive for B. melitensis, using the Rose Bengal test, complement fixation test and serum agglutination test, all of which are serology-based tests. The affected cattle were then isolated, sent to an abattoir and slaughtered as stipulated in the control programme of brucellosis in animals of South Africa - Animal Diseases Act (Act No. 35 of 1984 ss. 9.1, 9.2, 11). The farmer was instructed to send his milk to another local farm for pasteurisation until this farmer was able to pasteurise effectively on his own farm.
The patient was treated with doxycycline 100 mg twice daily and rifampicin 600 mg daily for six weeks. He commenced treatment in the first week of November 2016. The treatment was initiated by the clinicians in his hometown and it was uncertain why he was started on the treatment six weeks following the initial blood culture result. Soon after commencing with treatment, the patient reported side effects which included abdominal pain and vomiting. These were managed symptomatically, and the patient was able to complete treatment. The affected patient's family was tested serologically for brucellosis and were found to be negative. Prophylaxis was given to those family members who consented to receive it.
The United States Centers for Disease Control and Prevention's brucellosis laboratory exposure risk stratification tool was used to screen for exposed staff and staff exposures were stratified as minimal risk, low risk and high risk using these guidelines. Twenty-one of seventy-two staff members were identified, who had either directly handled the specimen on an open bench or were within 1.5 metres of the person who handled the specimen on an open bench, thus rendering them at high risk for acquiring brucellosis. Baseline serology was performed on all potentially exposed staff members and standard prophylaxis was provided by the employer. This comprised of rifampicin 600 mg oral daily for three weeks as well as doxycycline 100 mg twice daily for three weeks. One staff member was pregnant (in her second trimester) at the time, and subsequently received trimethroprim-sulfamethoxazole (160/800 mg) twice daily for three weeks. Exposed staff were advised to undergo follow-up serology at 0, 6, 12, 18 and 24 weeks post-exposure. Weekly symptom watch forms were completed and daily fever self-checks were done for six weeks as recommended by the Centers for Disease Control and Prevention and the World Health Organization. None of the staff members reported any symptoms for the duration of the symptom check.