Brief Report: Latent Tuberculosis Infection Among Sailors and Civilians Aboard U.S.S. Ronald Reagan --- United States, January--July 2006

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Crews aboard ships live and work in crowded, enclosed spaces. Historically, large tuberculosis (TB) outbreaks and extensive transmission of Mycobacterium tuberculosis have occurred on U.S. Navy ships (1,2). On July 13, 2006, smear- and culture-positive, cavitary, pulmonary TB was diagnosed in a sailor aboard the aircraft carrier U.S.S. Ronald Reagan; the patient, aged 32 years, had a negative human immunodeficiency virus test. The M. tuberculosis strain cultured was susceptible to all first-line TB medications. The sailor was born in the Philippines, had latent tuberculosis infection (LTBI)* diagnosed in 1995 shortly after enlisting in the U.S. Navy, and completed the 6-month daily isoniazid course that was standard treatment at that time (current treatment standard is 9 months). This report describes the contact investigation conducted by the U.S. Navy and CDC and demonstrates the importance of timely diagnosis of TB, identification and treatment of new LTBI, and cooperation among local, state, and federal agencies during large contact investigations.

During January 4--July 6, 2006, U.S.S. Ronald Reagan deployed with approximately 5,000 sailors aboard. Approximately 3,350 sailors were assigned to the ship's company and 1,630 to the air wing. During June 29--July 6, a total of 1,225 family members and friends of sailors (i.e., temporary civilian guests) boarded the ship in Hawaii and sailed to California. Short cruises for civilians are a tradition in the U.S. Navy; this 1-week trip marked the end of deployment for U.S.S. Ronald Reagan and its return to its home port of San Diego. During the cruise, civilians slept in the same quarters as sailors.

The patient was assigned to the air wing of the ship and received the diagnosis of TB on July 13. The next day, the U.S. Navy initiated a contact investigation.

Annual tuberculin skin tests (TSTs) are mandatory for all deployable naval personnel; therefore, documented baseline TST results were available for comparison. Among sailors designated as close contacts of the patient, 12 (4%) of 320 had new positive TST results. The U.S. Navy expanded the contact investigation to include all sailors and civilians who were aboard the ship >48 hours after February 20, 2006, the estimated start date of the patient's infectious period (3). The U.S. Navy contacted CDC for assistance with the civilian contact investigation.

All sailors were screened for TB, and the ship environment was assessed. To prioritize civilians for TB screening, a case-control study was conducted among sailors to identify factors associated with a new positive TST result. The patient was interviewed about personal, social, and occupational activities during the ship's deployment. A questionnaire was developed to collect information on potential exposure factors among study participants. A case was defined as a >5-mm increase in TST induration (localized swelling) diameter compared with the most recent TST result in a sailor aboard the U.S.S. Ronald Reagan during January--July 2006. A control was defined as a <5-mm increase in TST induration diameter compared with the most recent TST result in a sailor aboard the ship during the same period. To decrease misclassification of outcome status, all sailors with previous positive TST results were excluded from the study.

No additional TB disease^§was identified in sailors (4). However, 139 (3%) sailors had new positive TST results (indicating LTBI); all began isoniazid treatment for LTBI. A total of 123 (88%) sailors had TST results that met the case definition and were included in the study; 47 (38%) were members of the ship's company, and 76 (62%) were members of the air wing. A total of 92 (75%) of 123 case-patients and 549 (69%) of 800 controls completed questionnaires. In multivariable analysis, after controlling for other exposure factors, two variables were significantly associated with a new positive TST result: 1) being born outside of the United States (adjusted odds ratio [AOR] = 2.8; 95% confidence interval [CI] = 1.6--5.1; p<0.001) and 2) being a member of the air wing (AOR = 2.9; CI = 1.8--4.6; p<0.001).

The patient and other air-wing sailors slept in an open-bay compartment with 120 bunks arranged in stacks of three; another compartment of the same size for air-wing sailors was adjacent and connected to the patient's compartment. The patient's bunk was approximately 18 feet from an air intake that exhausted directly overboard for odor control. Despite several months of potential exposure in a high-risk setting, results from screening of all sailors suggested limited transmission of M. tuberculosis on the ship. Case-control study results indicated that sailors assigned to the air wing were at greatest risk for having a new positive TST result. Sailors assigned to the air wing slept in the same berthing compartment as the patient or in one that was adjacent to the patient. These findings were used to prioritize the contact investigation among civilians.

Thirty-eight male civilians slept in the same berthing compartment as the patient (n = 31) or an adjacent compartment (n = seven). Thirty-six (95%) of the 38 civilians were screened; two (5%) refused screening. Thirty-three (92%) had negative TST results. Two (6%) had known previous positive TST results, and both had clinical evaluations negative for TB. One (3%) civilian aged 70 years had a 15-mm TST result 18 days postexposure; no baseline TST was available for comparison. A second round of TST screening for sailors and civilians at risk for exposure began September 14.

Reported by: Captain F Chapman, MD, Commander, Naval Air Forces, US Pacific Fleet, San Diego; Lieutenant N Martin, MS, Naval Hospital Lemoore, Lemoore; Lieutenant J McDowell, MD, Carrier Air Wing Fourteen, San Diego; Lieutenant Commander T O'Hara, MD, Lieutenant Commander K Carrigan, MD, Navy Environmental and Preventive Medicine Unit Five, San Diego, California. T Wofford, Office of Workforce and Career Development; Div of Tuberculosis Elimination, National Center for HIV, Viral Hepatitis, STDs, and Tuberculosis Prevention (proposed); S Deshpande, PhD, A Buff, MD, EIS officers, CDC.

References

* Persons with LTBI have a positive tuberculin skin test result, a normal chest radiograph, and no signs or symptoms of TB disease. Persons with LTBI are asymptomatic, do not feel ill, and cannot spread TB to others.

The U.S.S. Ronald Reagan's air wing includes sailors from eight aircraft squadrons that support carrier flight operations during deployments. The ship's company includes sailors who are permanently assigned to the ship.

^§Persons with clinical TB disease generally have a positive TST result and other signs and symptoms compatible with TB (e.g., an abnormal chest radiograph) or clinical evidence of current disease. Laboratory criteria for TB disease diagnosis include isolation of M. tuberculosis from a clinical specimen or demonstration of M. tuberculosis from a clinical specimen by nucleic acid amplification testing or demonstration of acid-fast bacilli in a clinical specimen when a culture has not been or cannot be obtained.

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