Investigation of Mycobacterium Tuberculosis Transmission Aboard the U.S.S. Ronald Reagan, 2006

By Buff, Ann M Deshpande, Swati J; Harrington, Theresa A; Wofford, Taylor S; O’Hara, Timothy W; Carrigan, Kenichi; Martin, Nicholas J; McDowell, Jackie C; Ijaz, Kashef; Jensen, Paul A; Lambert, Lauren A; Moore, Marisa; Oeltmann, John E

ABSTRACT Pulmonary tuberculosis (TB) was diagnosed in a sailor aboard the U.S.S. Ronald Reagan; an investigation was conducted to determine a screening strategy for 1,172 civilian passengers who were aboard during a temporary guest rider program. Sailors were screened for latent TB infection (LTBI) and TB disease. A case- control study was conducted among sailors to determine factors associated with new LTBI. No secondary TB disease was identified; 13% of close contacts had new LTBI. Factors associated with new LTBI among sailors were having been born outside the United States (adjusted odds ratio = 2.80; 95% confidence interval, 1.55-5.07) and being a carrier air wing member (adjusted odds ratio = 2.89; 95% confidence interval, 1.83-4.58). Among 38 civilian passengers berthed near the patient, 1 (3%) had LTBI. The investigation results indicated that Mycobacterium tuberculosis transmission was minimal and eliminated unnecessary TB screening for 1,134 civilians which saved public health resources. INTRODUCTION

Historically, U.S. Navy ships were common and efficient settings for occupational transmission of Mycobacterium tuberculosis infection due to large crews, enclosed compartments, and closed ventilation systems.1-3 However, over the last 20 years, only two U.S. Navy shipboard outbreaks of tuberculosis disease (TB) have been reported.4,5 Both TB outbreaks occurred during long deployments and transmission of M. tuberculosis among sailors was extensive. Secondary TB disease was diagnosed in 0.2% to 0.9% of sailors and new latent tuberculosis infections (LTBI) were identified in 25% to 28% of sailors screened with tuberculin skin testing (TST).4,5

Tuberculosis contact investigations involving passengers and crew exposed during travel on modes of mass transportation, including airplanes, trains, and school buses, have previously been reported.6- 11 On airplanes and school buses where transmission of M. tuberculosis has been reported, factors associated with transmission were the extent of the patient’s illness and duration or frequency of travel. Highly contagious patients with smear-positive cavitary disease, air flights over 8 hours, and exposure over weeks to months on a school bus have been linked to M. tuberculosis transmission to both passengers and crew.6,8,10,11

In January 2006, the aircraft carrier U.S.S. Ronald Reagan deployed for 6 months with 4,977 sailors aboard; 3,348 sailors were assigned to the ship’s company and 1,629 sailors were assigned to the carrier air wing (CAW). During the last week of deployment, 1,172 civilian passengers were invited aboard as guests for a 1- week cruise. Civilian passengers, who were family members and friends of sailors, embarked on June 29 in Honolulu, Hawaii, and disembarked on July 6 in San Diego, California. Civilian passengers slept in spaceavailable bunks in the same berthing compartments as sailors. On July 13, a sailor assigned to the CAW was diagnosed with smear-positive, cavitary, pulmonary TB; by then, civilian passengers had returned to their homes in almost every U.S. state and three foreign countries. The U.S. Navy subsequently requested assistance from the Centers for Disease Control and Prevention (CDC) to determine the extent of M. tuberculosis transmission among sailors and to recommend and implement a screening strategy for civilian passengers based on their risk for TB infection.

This report describes a large shipboard TB contact investigation and demonstrates the interaction between occupational risks for sailors and recreational risks for passengers.

METHODS

Medical Record Review and Patient Interview

The patient’s medical records were reviewed to summarize disease characteristics and to estimate the patient’s infectious period.12 We interviewed the patient to obtain a list of close contacts (e.g., sailors with whom he worked and socialized) and the locations he frequented.

Shipboard Screening for LTBI

The U.S. Navy’s TB control program requires one baseline TST upon induction for all sailors and an annual TST for those sailors in operational or deployable units.13 All sailors who were aboard ship during deployment were screened for TB and LTBI following the patient’s diagnosis. We defined a new positive TST result as a >/=5- mm increase in induration as compared to the sailor’s most recent TST result.12,13 Sailors with a past history of a positive TST result (>100 -mm induration) were screened clinically and with a chest radiograph.12,13

Environmental Evaluation

We qualitatively assessed airflow in the patient’s berthing and work compartments and mapped the bunk locations of all sailors and civilians assigned to the patient’s berthing compartment.

Case-Control Study

We conducted a case-control study among sailors to establish factors associated with a new positive TST result, indicative of recent M. tuberculosis transmission. A case was defined as a sailor aboard the U.S.S Ronald Reagan during January to July 2006 with a >/ =5-mm increase in TST induration as compared with his/her most recent TST result. A control was any sailor aboard the ship during the same time period with

Controls were selected by simple random sampling from a complete listing of all sailors aboard the ship during deployment. To detect an odds ratio of 2 for having a new positive TST result, a ratio of four controls to each case was required. Due to transfers, separations, and deployments in this highly mobile military population, controls were initially oversampled. Eight hundred controls were selected for participation. Study participation was voluntary; institutional review board approval was not required for this public health investigation.

We administered participants a 31-item questionnaire to collect information on demographics, berthing and workspace locations, communal locations (e.g., galleys), and time spent off the ship for liberty or temporary duty. Associations between dichotomous predictor variables of interest by case or control status were evaluated using odds ratios and 95% confidence intervals (CIs). Fisher’s exact test was used when appropriate. Associations between continuous predictor variables of interest by case or control status were evaluated using the Mann-Whitney U test. To adjust for the effects of multiple predictor variables, logistic regression models were it to include all variables during the initial construction which were significant at alpha = 0.1 in univariate analyses. Variables were removed from the model using backward elimination.

RESULTS

Medical Record Review and Patient Interview

The patient was a 32-year-old male who was born in the Republic of the Philippines and assigned to the CAW. Upon enlistment in July 1994, his TST result was 11 mm; treatment for LTBI was not started. The patient reported to his first duty station in December 1994; he had a 17-mm TST reaction and a negative chest radiograph. He completed the then standard 6 months of daily isoniazid (INH) treatment for LTBI in July 1995 based on patient report and medical records which included prescription refills and pill counts. In April 2006, the patient denied any symptoms consistent with TB during his annual symptom screening.

In early June 2006, he presented to the ship’s medical clinic with complaints of productive cough, fever, chills, headache, and general malaise for ~3 weeks. His temperature was 39.90C and his chest radiograph showed a right upper lobe (RUL) infiltrate. He was diagnosed with communityacquired pneumonia, treated with a fluoroquinolone antibi-. otic, and restricted for 1 week to his berthing compartment (sick-in-quarters). His symptoms improved over the following week.

Approximately 3 weeks later, the patient returned to clinic with continued productive cough and right-sided, pleuritic chest pain. He was afebrile and had expiratory wheezes on examination. A TST was placed and documented 48 hours later as negative at O mm. A repeat chest radiograph showed RUL consolidation. No sputum specimens were obtained. He was diagnosed with resolving community-acquired pneumonia and treated with a macrolide antibiotic.

One week later in July 2006, he returned to his provider with continued productive cough, chest wall pain, and weight loss of 6.4 kg over 4 weeks. He was treated with over-thecounter medications for symptom relief and placed on sickin-quarters status for the remainder of the deployment. He was also referred to the pulmonary medicine clinic after deployment for further evaluation.

On July 13, 1 week after the ship returned to port, the patient was diagnosed with pulmonary TB and was hospitalized. His sputum smear was positive for 4+ acid-fast bacilli, chest radiograph and computed tomography showed RUL posterior segment consolidation with marked cavitation, and human immunodeficiency virus serology was negative. His sputum cultures grew M. tuberculosis susceptible to all four first-line antituberculosis medications (isoniazid, rifampin, ethambutol, and pyrazinamide). The patient was treated with a standard four-drug, antituberculosis medication regimen by directly observed therapy. Based on the patient’s onset of symptoms in late May, we estimated that his infectious period started ~3 months previously in late February.12 Close Contact Investigation and Shipboard Screening

No TB disease was identified among 20 sailors named as close contacts. Among close contacts were the patient’s 5 immediate bunkmates and 13 workmates. Three (60%) bunkmates and two (15%) workmates had previous positive TST results; therefore, we could not determine recent infection status in these sailors (Fig. 1). Two (13%) of 15 close contacts had new positive TST results. Of the sailors with new positive TST results, one worked with and was mentored by the patient, and one was both a bunkmate and workmate of the patient. Both sailors subsequently completed INH treatment for LTBI.

The patient was not hospitalized on the ship’s medical ward but visited the ship’s clinic at least seven separate times and cumulatively spent over 20 hours in medical spaces while contagious. Among 50 medical personnel, none had new positive TST results.

A total of 134 (3%) of 4,524 sailors had new positive TST results; the median TST induration was 10 mm (range, 5-40 mm). All sailors started INH treatment. All 420 (8%) sailors with a history of positive TST results had negative clinical evaluations and chest radiographs for TB disease. Despite efforts to notify sailors who had separated from the U.S. Navy, we were unable to locate 33 (0.7%) sailors for screening.

Environmental Evaluation

The main focus of the evaluation was the patient’s berthing compartment and the adjacent berthing compartment. These two open bay berthing compartments were used exclusively by male sailors assigned to the CAW. The two berthing compartments were aligned front to back with openings to allow free movement of air between the compartments. One hundred twenty sailors were berthed in each compartment. The patient’s bunk was located ~20 feet from the main air exhaust unit (Fig. 1). The air exhaust unit was actively drawing air from the berthing space and had two large standard paniculate filters in place. The air exhaust duct ran through a toilet and shower compartment to the exterior of the ship. The air was not recirculated but rather exhausted overboard for odor control.

Case-Control Study

All 134 sailors with new positive TST results were initially considered for inclusion in the case-control study. Nine (7%) sailors were excluded from the study because their medical records were not available to confirm case status. One hundred twenty-five (93%) sailors were eligible for inclusion as cases; 92 (74%) cases and 549 (69%) controls completed questionnaires. Sailors were not available for questionnaire administration due to leave, deployment, transfer, separation, or declined participation.

Univariate analysis demonstrated that cases were more likely to be of Hispanic or Asian race/ethnicity, born outside of the United States, and members of the CAW as compared with controls (Table I). No continuous variables were significantly associated with increased odds of a new positive TST result (Table II).

Multivariable analysis suggested that those sailors born outside the United States (adjusted odds ratio, 2.80; 95% CI, 1.55-5.07, p

Civilian Passenger Screening

Because no secondary TB disease was identified among close contacts or other sailors and because the patient was restricted to his berthing compartment during the week that civilian passengers were aboard, we recommended and implemented TB screening for only those civilians who shared the same or adjacent berthing compartments as the patient. Thirty-eight civilian passengers slept in the two berthing compartments; one slept directly across from the patient. Their median age was 48 years with a range from 9 to 70 years. All were male and born in the United States.

Thirty-six (95%) of 38 civilian passengers were screened, and two (5%) refused (Table III). No secondary TB disease was identified among them. One (3%) U.S.-born, 70-year-old male had a 15-mm TST result; he did not have a previous TST result for comparison. His clinical evaluation was negative. All other civilian passengers had either negative TST results or negative clinical evaluations including chest radiographs.

DISCUSSION

The U.S. Navy and CDC conducted this comprehensive investigation to determine a screening strategy for civilian passengers who were exposed to the patient with TB disease aboard ship. The situation was complicated by the large number of civilian passengers who were located in 47 U.S. states and at least three foreign countries. We reviewed the close contact investigation and shipboard screening results, evaluated environmental conditions aboard ship, and conducted a case-control study among sailors who were aboard ship with the contagious patient during a 6-month deployment, to determine factors associated with a new positive TST result, indicative of recent M. tuberculosis transmission.

The close contact investigation and shipboard screening revealed no secondary cases of TB disease, and 13% of the patient’s close contacts and 3% of all sailors had new positive TST results; generally, 20% to 30% of named close contacts have positive TST results during TB contact investigations.13 The environmental evaluation showed that air from the patient’s sleeping quarters was exhausted overboard without being recirculated. Finally, the case- control study found that sailors assigned to the CAW and those who were born outside of the United States had an increased likelihood of having new positive TST results as compared with other sailors. Because the patient was a member of the CAW and shared berthing and work locations with other CAW sailors, it is reasonable that members of the CAW were at increased risk of TB infection. Being born in a country with a high TB prevalence is a well-known risk factor for both LTBI and TB disease.14-16 However, all sailors, regardless of birthplace, were previously tested, and those with a history of positive TST results were excluded from the study. Therefore, new positive TST results in these sailors likely represents recent transmission of M. tuberculosis.

Results from each component of the investigation provided evidence that there was limited transmission of M. tuberculosis to sailors aboard the ship during the 6-month deployment and, therefore, likely minimal risk of TB infection among civilian passengers who were aboard for 1 week. Based on these conclusions, we recommended screening only the 38 civilian passengers berthed in the same or adjacent berthing compartments as the patient rather than all 1,172 civilian passengers. Although sharing the same or adjacent berthing compartment as the patient was not found to be a significant risk factor, many of the sailors who were berthed closest to the patient had a history of positive TST results, and, therefore, not included in the case-control study. As a result, the case-control study may have underestimated the risk of M. tuberculosis transmission to sailors berthed in the same or adjacent compartments as the patient.

Only one (3%) civilian passenger had a positive TST result at 18 days after exposure; since this passenger did not have a previous TST result for comparison, we cannot determine if this represents recent transmission or previous undiagnosed LTBI. The estimated prevalence of LTBI in the general population is 4%.17 By prioritizing civilian passengers for TB screening based on risk for infection, we eliminated unnecessary TB screening for 1,134 low- risk people and prevented unnecessary LTBI treatment for those who would have had false-positive TST results. This approach saved limited public health resources by targeting the small number of civilian passengers at risk for infection.

There were two main limitations of the case-control study. Nine (7%) sailors with new positive TST results were excluded from study participation as a result of insufficient data to determine case status; all those excluded were from the CAW. Only 74% of the eligible cases completed questionnaires; more cases from the ship’s company (81%) completed questionnaires compared with the CAW (69%). Consequently, both limitations differentially affected CAW sailors and may have led to an underestimation of the true association between having a new positive TST result and being a member of the CAW.

Two other observations from this investigation deserve mention. The first is the patient’s delayed TB diagnosis. Diagnosis of pulmonary TB disease is commonly delayed, particularly in low- incidence settings.18 Tuberculosis in the U.S. Navy is relatively rare; fewer than two cases of TB disease per 100,000 persons are diagnosed annually.19 In addition, the patient was initially treated with a fluoroquinolone antibiotic for community-acquired pneumonia; fluoroquinolone antibiotics have excellent bactericidal activity against M. tuberculosis.20,21 Failing to consider TB in the differential diagnosis of upper lobe pneumonia-particularly when fluoroquinolones are initially prescribed with resulting temporary clinical improvement-can significantly delay the diagnosis of TB and initiation of antituberculosis treatment.22,23

The second observation was the misinterpretation of the patient’s TST result. A negative TST reaction does not exclude the diagnosis of TB disease in patients with signs and symptoms consistent with TB disease. Up to 25% of patients with TB disease will have negative TST results when tested during the diagnostic evaluation.24,25 Patients with TB disease may have a diminished ability to mount a delayed-hypersensitivity reaction to tuberculin antigens because of depressed immune function. The inability to react to skin tests is termed anergy and may be caused by conditions or medications associated with immunosuppression (e.g., human immunodeficiency virus infection, chronic renal failure, solid organ transplant, the equivalent of 15 mg of prednisone per day, tumor necrosis factor alpha antagonists). Skin tests for anergy (i.e., control antigens) have poor predictive value and are no longer recommended. In this patient with a known previous 17-mm TST reaction in 1995, a TST should not have been placed. However, when the patient’s TST reaction was negative, the result should have prompted an evaluation for TB disease. And although treatment of LTBI with 6 months of INH reduces the subsequent incidence of TB by up to 70%, patients with a history of treated LTBI remain at risk for TB disease throughout their lifetimes.26,27 Despite a delay in diagnosis and several months of potential exposure to a contagious patient, M. tuberculosis transmission aboard the U.S.S. Ronald Reagan was limited. In addition, civilians who shared a berthing compartment with the patient were no more likely than the general population to have a positive TST result. Both U.S. Navy ships and passenger cruise ships have sailors and crew members from TB-endemic countries, and occasionally a sailor or crew member is diagnosed with TB disease even on ships with rigorous TB control programs. This investigation suggests that results from shipboard contact investigations, where sailors and crew members have documented baseline TST results, can be used to guide decisions regarding TB screening of passengers under similar circumstances. In this particular situation, mass screening of passengers was unnecessary because their risk for infection was minimal. Decisions to conduct future investigations in similar settings should take into consideration the activities of the contagious TB patient, potential for infection through shared airspace, and available public health resources.

REFERENCES

1. Hardy MA, Schmidek HH: Epidemiology of tuberculosis aboard a ship. JAMA 1968; 203: 109-13.

2. Houk VN, Baker JH, Sorensen K, Kent DC: The epidemiology of tuberculosis infection in a closed environment. Arch Environ Health 1968; 16: 25-35.

3. Houk VN, Kent DC, Baker JH, Sorensen K, Hanzel GD: The Byrd study: in-depth analysis of a micro-outbreak of tuberculosis in a closed environment. Arch Environ Health 1968; 16: 4-6.

4. DiStasio AJ, Trump DH: The investigation of a tuberculosis outbreak in the closed environment of a U.S. Navy ship, 1987. Milit Med 1990; 155; 347-51.

5. LaMar JE, Malakooti M: Tuberculosis outbreak investigation of a U.S. Navy amphibious ship crew and the marine expeditionary unit aboard, 1998. Milit Med 2003; 168: 523-7.

6. Driver CR, Valway SE, Morgan WM, Onorato IM, Castro KG: Transmission of Mycobacterium tuberculosis associated with air travel. JAMA 1994; 272: 1031-5.

7. Centers for Disease Control and Prevention: Exposure of passengers and flight crew to Mycobacterium tuberculosis on commercial aircraft, 1992-1995. MMWR Morb Mortal Wkly Rep 1995; 44: 137-40.

8. Kenyon TA, Valway SE, Ihle WW, Onorato IM, Castro KG: Transmission of multidrug-resistant Mycobacterium tuberculosis during a long airplane flight. N Engl J Med 1996; 334: 933-8.

9. Moore M, Valway SE, Ihle W. Onorato IM: A train passenger with pulmonary tuberculosis: evidence of limited transmission during travel. Clin Infect Dis 1999; 28: 52-6.

10. Yusuf HR, Braden CR, Greenberg AJ, Weltman AC, Onorato IM, Valway SE: Tuberculosis transmission among five school bus drivers and students in two New York counties. Pediatrics [serial online] 1997; 100: E9. Available at http://www.pediatrics.Org/cgi/content/ full/100/3/ e9; accessed April 30, 2007.

11. Curtis AB, Ridzon R, Vogel R, et al: Extensive transmission of Mycobacterium tuberculosis from a child. N Engl J Med 1999; 341: 1491-5.

12. Centers for Disease Control and Prevention: Guidelines for the investigation of contacts of persons with infectious tuberculosis: recommendations from the National Tuberculosis Controllers Association and the CDC. No. RR-15. MMWR Morb Mortal Wkly Rep 2005; 54: 1-47.

13. Bureau of Medicine and Surgery: BUMED Instruction 6224.8: Tuberculosis Control Program. Philadelphia, PA, Naval Publications and Forms Directorate, September 14, 1993.

14. American Thoracic Society and Centers for Disease Control and Prevention: Core Curriculum on Tuberculosis, Ed 4. Atlanta, GA, Department of Health and Human Services, 2000.

15. Talbot EA, Moore M, McCray E, Binkin NJ: Tuberculosis among foreign-born persons in the United States, 1993-1998. JAMA 2000; 284: 2894-900.

16. Zuber PL, McKenna MT, Binkin NJ, Onorato IM, Castro KG: Longterm risk of tuberculosis among foreign-born persons in the United States. JAMA 1997; 278: 304-7.

17. Bennett DE, Courval JM, Onorato IM, et al: Prevalence of tuberculosis infection in the U.S. population: the national health and nutrition examination survey, 1999-2000. Am J RespirCrit Care Med 2008; 177: 1-8.

18. Golub JE, Bur S, Cronin WA, et al: Patient and health care system delays in pulmonary tuberculosis diagnosis in a low- incidence state. Int J Tuberc Lung Dis 2005; 9: 992-8.

19. Gamble-Lawson C, Bowman C, Bowman W, Riegodedios A, Bohnker B: Tuberculosis in the U.S. Navy and Marine Corps: a 4-year retrospective analysis 2000-2003. Navy Med Surveill Rep: 2004; 7: 6- 9.

20. De Souza MV, Vasconcelos TR, de Almeida MV, Cardoso SH: Fluoroquinolones: an important class of antibiotics against tuberculosis. Curr Med Chem 2006; 13: 455-63.

21. Johnson JL, Hadad DJ, Boom WH, et al: Early and extended early bactericidal activity of levofloxacin, gatifloxacin and moxifloxacin in pulmonary tuberculosis. Int J Tuberc Lung Dis 2006; 10: 605-12.

22. Yoon YS, Lee HJ, Yoon HI, et al: Impact of fluoroquinolones on the diagnosis of pulmonary tuberculosis initially treated as bacterial pneumonia. Int J Tuberc Lung Dis 2005; 9: 1215-19.

23. Dooley KE, Golub J, Goes FS, Merz WG, Sterling TR: Empiric treatment of community-acquired pneumonia with fluoroquinolones, and delays in the treatment of tuberculosis. Clin Infect Dis 2002; 34: 1606-12.

24. Holden M, Dubin MR, Diamond PH: Frequency of negative intermediate-strength tuberculin sensitivity in patients with active tuberculosis. N Engl J Med 1971; 285: 1506-09.

25. Nash DR, Douglass JE: Anergy in active pulmonary tuberculosis: a comparison between positive and negative reactors and an evaluation of 5 TU and 250 TU skin test doses. Chest 1980; 77: 32-7.

26. Comstock GW, Ferebee SH, Hammes LM: A controlled trial of community-wide isoniazid prophylaxis in Alaska. Am Rev Respir Dis 1967; 95: 935-43.

27. International Union Against Tuberculosis Committee on Prophylaxis: Efficacy of various durations of isoniazid preventive therapy for tuberculosis: five years of follow-up in the IUAT trial. Bull World Health Organ 1982; 60: 555-64.

LCDR Ann M. Buff, USPHS*[dagger]; Swati J. Deshpande, PhD*[double dagger]; CDR Theresa A. Harrington, USPHS[dagger]; Taylor S. Wofford, MD[section]; LCDR Timothy W. O’Hara, MC USN[para]; LCDR Kenichi Carrigan, MC USNJ[para]; LT Nicholas J. Martin, MSC USN||; LT Jackie C. McDowell, MC USN#; Kashef Ijaz, MD[dagger]; CAPT Paul A. Jensen, USPHS[dagger]; Lauren A. Lambert, MPHf; CDR Marisa Moore, USPHS[dagger][double dagger]; John E. Oeltmann, PhD[dagger]

* Epidemic Intelligence Service, Office of Workforce and Career Development, Centers for Disease Control and Prevention, 1600 Clifton Road, NE, MS E-92, Atlanta, GA 30333.

[dagger] Division of Tuberculosis Elimination, CDC, 1600 Clifton Road, NE, MS E-10, Atlanta, GA 30333.

[dagger] County of San Diego Health and Human Services Agency, 3851 Rosecrans Street, San Diego, CA 92110.

[section] The CDC Experience Fellow, Office of Workforce and Career Development, CDC, 1600 Clifton Road, NE, MS E-92, Atlanta, GA 30333.

[para] U.S. Navy Environmental and Preventive Medicine Unit Five, 3235 Albacore Alley, San Diego, CA 92136.

|| U.S. Naval Hospital Lemoore, 937 Franklin Avenue, Lemoore, CA 93243.

# Carrier Air Wing Fourteen, Branch Medical Clinic, Naval Air Station North Island, Box 357046, San Diego, CA 92135-7046.

This manuscript was received for review in December 2007. The revised manuscript was accepted for publication in March 2008.

ACKNOWLEDGMENTS

We thank the sailors and officers of the U.S.S. Ronald Reagan, Carrier Air Wing Fourteen, Commander, Naval Air Forces, U.S. Pacific Fleet, and U.S. Navy Environmental and Preventive Medicine Unit Five for their participation. We also thank the state tuberculosis controllers and local health departments for their support in this investigation.

Dr. Taylor S. Wofford is a fellow of The CDC Experience, a 1- year fellowship in applied epidemiology at the CDC, funded by Pfizer Public Health Group through the CDC Foundation.

Copyright Association of Military Surgeons of the United States Jun 2008

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