METHODS: Multnomah County Health Department (MCHD) investigated close and casual contacts. Close contact was defined as any presence in the elephant barn or being within 15 feet of any of the elephants in the enclosed outdoor area at least weekly. Casual contacts included employees or volunteers who might have been exposed to elephant trunk secretions or fecal matter but did not have close contact with the elephants.
RESULTS: Nineteen close contacts and 59 casual contacts were identified. Six of the 19 close contacts had positive Tuberculin Skin Tests (TSTs); none had active disease. Among the casual identified, 48 (81%) were fully evaluated; none had a positive result. In the course of the investigation, two other elephants, elephant B and C, had positive trunk wash cultures, in October 2013 and May 2014, respectively. In October 2013, MCHD discovered that patient A, who had completed treatment for pleural TB in the fall of 2012, had been a casual contact of elephant A. Patient A had worked at the zoo during 2012, but had limited contact with elephants. Isolates from patient A and elephant A were analyzed at CDC using whole genome sequencing. Comparison of the genomes identified no differences. Because the strain isolated from patient A matched that from elephant A, MCHD staff searched for an unidentified source. The investigation was expanded to include 1) all close contact employees who had worked at the zoo since January 1, 2010 and 2) people who participated in the same February 2012 zoo orientation as patient A. Among the 28 persons who participated in the 2012 zoo orientation, 18 (68%) were tested and had a negative TST. Final results of the investigation of all 31 close contacts since 2010 identified one additional positive TST result from July, 2011; this is close to the zoo’s baseline annual conversion number of 0–1 per year. Based on these findings, shedding of M. tuberculosis by elephants before elephant A’s diagnosis is considered unlikely.
CONCLUSIONS: Genotyping surveillance, in conjunction with epidemiologic investigation, may also be effective in linking human and non-human TB cases and evaluating unrecognized transmission. Collaboration between public health, veterinary medicine, and occupational health is needed to better understand the risks and to prevent zoonotic transmission of M. tuberculosis.