ORIGINAL STUDIES Measles Outbreak Associated With an International Youth Sporting Event in the United States, 2007 Tai-Ho Chen, MD,*† Preeta Kutty, MD, MPH,‡ Luis E. Lowe, MS,‡ Elizabeth A. Hunt, RN, MPH,† Joel Blostein, MPH,§ Rita Espinoza, MPH,¶ Clare A. Dykewicz, MD, MPH, Susan Redd,‡ Jennifer S. Rota, MPH,‡ Paul A. Rota, PhD,‡ James R. Lute, PhD,† Perrianne Lurie, MD, MPH,† Michael D. Nguyen, MD,* ** Ma `ria Moll, MD,† Susan E. Reef, MD,†† Julie R. Sinclair, DVM, MPH, William J. Bellini, PhD,‡ Jane F. Seward, MB BS,‡ and Stephen M. Ostroff, MD† Background: Despite elimination of endemic measles in the United States (US), outbreaks associated with imported measles continue to occur. In 2007, the initiation of a multistate measles outbreak was associated with an imported case occurring in a participant at an international youth sporting event held in Pennsylvania. Methods: Case finding and contact tracing were conducted. Control measures included isolating ill persons and administering postexposure prophylaxis to exposed persons without documented measles immunity. Laboratory evaluation of suspected cases and contacts included measles serologic testing, viral culture, detection of viral RNA by reverse-transcrip- tion polymerase chain reaction, and viral genotyping. Results: The index case occurred in a child from Japan aged 12 years. Contact tracing among 1250 persons in 8 states identified 7 measles cases; 5 (71%) cases occurred among persons without documented measles vaccination. Epidemiologic and laboratory investigation supported a single chain of transmission, linking the outbreak to contemporaneous measles virus genotype D5 transmission in Japan. Of the 471 event participants, 193 (41%) lacked documentation of presumed measles immunity, 94 (49%) of 193 were US-resident adults, 19 (10%) were non-US-resident adults (aged 18 years), and 80 (41%) were non-US-resident children. Discussion: Measles outbreaks associated with imported disease are likely to continue in the US. Participants in international events, international travelers, and persons with routine exposure to such travelers might be at greater risk of measles. To reduce the impact of imported cases, high measles, mumps, and rubella vaccine coverage rates should be maintained throughout the US, and support should continue for global measles control and elimination. Key Words: measles, disease outbreaks, genotype classification, travel, sports (Pediatr Infect Dis J 2010;29: 794 – 800) M easles is a highly infectious acute viral illness that caused an estimated 242,000 deaths in 2006, mostly in developing countries. 1 In the United States (US) during the decade before the 1963 introduction of measles vaccine, 500,000 measles cases and 450 associated deaths were reported (with an estimated 4 million total US cases) annually. 2 Endemic measles transmission in the US was declared interrupted in 2000 as a result of high coverage rates with 2 doses of measles, mumps, and rubella (MMR) vaccine and effective surveillance and outbreak re- sponse. 3,4 However, measles outbreaks have continued in the US among persons exposed to imported cases. 5–8 On August 16, 2007, measles was diagnosed in a Japanese participant at a 10-day international youth sporting event held annually in Pennsylvania, with an estimated cumulative attendance of 265,000. We describe the subsequent outbreak, investigation, and response involving local, state, and federal public health staff in 8 states. SUBJECTS AND METHODS When the index case of measles was reported to the Penn- sylvania Department of Health, public health authorities initiated a multistate investigation because of the patient’s travel history and international event participation. The 2007 Council of State and Territorial Epidemiologists measles case definitions (Table 1) were used. 9 Epidemiologic investigation involved case finding, contact tracing, and implementation of control measures. These included isolation of patients and administration of postexposure prophy- laxis (MMR vaccine or immunoglobulin) to contacts who lacked evidence of presumptive measles immunity through documented vaccination, laboratory evidence of immunity, history of physi- cian-diagnosed measles, or birth before 1957 (Table 2). 10 Vacci- nation status was sought from sources including parents, immuni- zation cards, schools, and healthcare providers. Persons were considered vaccinated if vaccinations were recorded with docu- mented dates. To identify aircraft-associated exposures, flight manifests were requested and contact information was obtained for passengers seated within 1 row of the index patient on the same side of an airplane aisle, according to the Centers for Disease Control and Prevention (CDC) protocols at the time of the inves- tigation. Passenger contact information was forwarded to state health departments. Data analysis was conducted using EpiInfo version 3.3.2 (CDC, Atlanta, GA).  2 and Fisher exact test tests were applied to categorical variables; t test was used for continu- ous variables. Accepted for publication March 2, 2010. From the *Epidemic Intelligence Service, Centers for Disease Control and Prevention, Atlanta, GA; †Pennsylvania Department of Health, Harrisburg, Pennsylvania, PA; ‡Division of Viral Diseases, Centers for Disease Control and Prevention, Atlanta, GA; §Michigan Department of Community Health, Lansing, MI; ¶Texas Department of State Health Services, Austin, TX; Division of Global Migration and Quarantine, Centers for Disease Control and Prevention, Atlanta, GA; **Philadelphia Department of Public Health, Philadelphia, PA; and ††Global Immunization Division, Centers for Disease Control and Prevention, Atlanta, GA. The findings and conclusions in this article are those of the authors and do not necessarily represent the views of the Centers for Disease Control and Prevention. Use of trade names and commercial sources is for identification purposes only and does not imply endorsement by the Public Health Service or the U.S. Department of Health and Human Services. Presented, in part, at the 42nd National Immunization Conference, March 18, 2008, Atlanta, GA. Address for correspondence: Tai-Ho Chen, Centers for Disease Control and Prevention, CDC Honolulu Airport Quarantine Station, 300 Rodgers Blvd 67, Honolulu, HI 96819. E-mail: tchen2@cdc.gov or Preeta Kutty, Centers for Disease Control and Prevention, 1600 Clifton Rd, MS A-47, Atlanta, GA 30333. E-mail: pkutty@cdc.gov. Copyright © 2010 by Lippincott Williams & Wilkins ISSN: 0891-3668/10/2909-0794 DOI: 10.1097/INF.0b013e3181dbaacf The Pediatric Infectious Disease Journal • Volume 29, Number 9, September 2010 794 | www.pidj.com