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Measles Outbreak Among School-Aged Children -- Juneau, Alaska, 1996

An outbreak of measles among school-aged children occurred in Juneau, Alaska, from February 16 through April 25, 1996. Of 63 confirmed cases * , 47 were serologically confirmed, and virus was cultured from 15; a total of 41 (65%) were among school-aged children (i.e., aged 6-18 years). This report summarizes results of the epidemiologic investigation conducted by the Division of Public Health, Alaska Department of Health and Social Services (ADPH), which found evidence of measles transmission at schools despite high rates of coverage with one dose of measles-containing vaccine (MCV).

The first five cases occurred among four students and a teacher at an elementary school; all had rash onset during February 16-19. The 63 case-patients ranged in age from 8 months to 45 years (median: 11 years): one was aged less than 1 year; 10 (16%), 1-4 years; 41 (65%), 5-19 years; and 11 (18%), greater than or equal to 20 years. Two persons with measles were hospitalized, including a child with dehydration and an adult with neutropenia. Measles virus was isolated from nasopharyngeal specimens obtained from 15 patients and from urine specimens from three of these same patients; isolates were genotypically similar to viruses recently isolated from Europe but different from isolates circulating in the United States during 1989-1992 (1).

Probable sites of measles acquisition were school (31 {49%}), home (14 {22%}), indoor soccer games (seven {11%}), and other settings (six {10%}); the site was unknown for five (8%). Cases were more likely to have been acquired at school during the first 35 days of the outbreak (19 {59%} of 32) than during the remaining 35 days (12 {39%} of 31).

Cases occurred among 40 students and four faculty members at seven of eight public schools in Juneau; one case occurred in a student at a private school. School-specific incidence rates were highest at the high school annex ** (five {4%} of 127), a middle school (15 {2%} of 687), and the elementary school attended by the index patient (seven {1%} of 525). At the beginning of the 1995-96 school year, approximately 99% of 5400 public school children in Juneau had received at least one dose of MCV. The number of children who had received more than one dose of MCV was unknown; however, a second dose of measles-mumps-rubella vaccine (MMR) for school-aged children enrolled in public or private school was not required in Alaska at the time of the outbreak.

Of the 63 case-patients, 33 (52%) had received only one dose of MCV on or after their first birthday, and 30 (48%) had never been vaccinated with MCV. Among the 30 who were not vaccinated, 24 (80%) were eligible to be vaccinated (i.e., aged greater than or equal to 12 months and born on or after January 1, 1957); of the 24 who were eligible to be vaccinated, all 12 school-aged children had religious exemptions, and two of nine children aged 1-4 years were siblings of these unvaccinated schoolchildren.

Although no source case was identified, this outbreak coincided with a measles outbreak associated with the Seattle-Tacoma (Washington) airport, the major airport gateway to Juneau. The first three case-patients in the Seattle area had onset of measles during February 2-4, 1996; these cases occurred among two airport workers and an airport visitor who, on January 20, were at the Seattle-Tacoma airport concourse of the main airline serving Juneau. Because measles transmission probably occurred in the airport on January 20, a Juneau-bound passenger also may have been exposed and may have become the source case for the Juneau outbreak. Isolates from the Seattle cases were not available for comparison.

Measures to control the outbreak were implemented beginning February 17 and included efforts to vaccinate school-aged children and contacts of persons with suspected cases with at least one dose of MCV; active surveillance for rash illness in doctor's offices, schools, and the one hospital emergency department in Juneau; and weekly fax transmissions of outbreak updates to health-care providers and public health nurses in Juneau and all other areas of southeast Alaska. As a result of this outbreak, ADPH is requiring all Alaska schoolchildren in kindergarten and first grade to receive a second dose of MCV for school entry.

Reported by: P Rohrbacher, K Miller, MPH, L Cameron, M Lexon, C See, K Slotnick, J Miller, M O'Bryan, G Herriford, K Glass, T Schmidt, MS, W Evans, P Kunkel, B Bond, MS, J Maddux, DVM, M Masters, PhD, M Westcott, D Ritter, S Kew, L Wood, MPA, G Yett, SA Jenkerson, MSN, M Schloss, MPH, E Funk, MD, M Beller, MD, P Nakamura, MD, JP Middaugh, MD, State Epidemiologist, Div of Public Health, Alaska Dept of Health and Social Svcs. J Boase, MS, Seattle-King County Health Dept, Seattle; B Lamont, Washington Dept of Health. Measles Virus Section, Respiratory and Enterovirus Br, Div of Viral and Rickettsial Diseases, National Center for Infectious Diseases; Measles Activity, Child Vaccine Preventable Disease Br, Div of Epidemiology and Surveillance, National Immunization Program; Div of Applied Public Health Training (proposed), Epidemiology Program Office, CDC.

Editorial Note

Editorial Note: In this measles outbreak, the large number of cases among school-aged children was attributed primarily to sustained transmission in schools characterized by high coverage levels with one dose of MCV. Before this outbreak, no measles transmission had been documented in Alaska schools since 1976, and approximately 99% of Juneau schoolchildren had received at least one dose of MCV; however, outbreaks have occurred previously among school-aged children vaccinated with one dose of MCV (2). In addition, consistent with outbreaks that occurred in the United States during 1995, viral isolates from cases in Juneau were genotypically similar to viruses recently isolated outside the United States and were not related to viruses that circulated during the measles resurgence in the United States during 1989-1992 (1). This finding suggests that recent outbreaks have resulted from importation of measles with subsequent transmission in the United States (1).

In 1989, as a result of continued measles outbreaks among school-aged children vaccinated with one dose of MCV, the Advisory Committee on Immunization Practices (ACIP) and the American Academy of Pediatrics recommended a routine two-dose measles vaccination schedule. In addition, ACIP recommended that, during outbreaks, a second dose of MCV be administered to children who had received only one dose of MCV before the outbreak (3). A measles outbreak (i.e., one case of confirmed measles in a community) should prompt vaccination of potentially susceptible persons. During school outbreaks, revaccination with MMR in affected schools is recommended. Revaccination consists of providing a second dose of MCV to all students, their siblings, and school personnel who were born during or after 1957 and do not have documented receipt of two doses of MCV on or after their first birthday or evidence of measles immunity (3). Revaccination also should be strongly considered in unaffected schools within the same community. The extensiveness of revaccination programs may vary with the magnitude of interaction at sporting and other interscholastic events and should strongly be considered when children in more than two schools are affected.

A routine two-dose MCV schedule for school-aged children will protect almost all of the estimated 2%-5% of children who do not respond to the first dose (4). The first dose of MCV should be given at age 12-15 months and the second dose at age 4-6 years or 11-12 years (3). Efforts to vaccinate the entire school-aged population in the United States with two doses of MCV are necessary to decrease the number and size of future measles outbreaks and to achieve elimination of measles in the United States. The speed at which this occurs locally depends on when two-dose MCV requirements were implemented in each state and the number of cohorts covered by the requirement. Forty-two states, including Alaska, require at least one school-grade cohort to be vaccinated with two doses of MCV. ACIP is revising recommendations for measles prevention that will encourage all states to achieve full coverage with two doses of MCV for all school-aged children in kindergarten through 12th grade by 2001.

Implementation of the two-dose strategy has been important in reducing measles incidence levels to current record low levels. In Finland, measles transmission was successfully eliminated following initiation of a two-dose MMR vaccination program in 1982 (5), similar in concept to the U.S. strategy. Countries of the Western Hemisphere, with the technical assistance of the Pan American Health Organization, have reduced measles incidence more than 95% by using a strategy based on periodic mass vaccination campaigns (6). These successful efforts to control measles outside the United States are important because long-term success in measles-control efforts in the United States and other countries require strengthened global control of measles.

References

  1. CDC. Measles -- United States, 1995. MMWR 1996;45:305-7.

  2. Gustafson TL, Lievens AW, Brunell PA, Moellenberg RG, Buttery CM, Sehulster LM. Measles outbreak in a fully immunized secondary-school population. N Engl J Med 1987;316:771-4.

  3. CDC. Measles prevention: recommendations of the Immunization Practices Advisory Committee (ACIP). MMWR 1989;38(no. S-9).

  4. Watson JC, Pearson JA, Markowitz LE, et al. An evaluation of measles revaccination among school-entry-aged children. Pediatrics 1996;97:613-8.

  5. Peltola H, Heinonen OP, Valle M, et al. The elimination of indigenous measles, mumps, and rubella from Finland by a 12-year, two-dose vaccination program. N Engl J Med 1994;331:1397-402.

  6. de Quadros CA, Olive JM, Hersh BS, et al. Measles elimination in the Americas: evolving strategies. JAMA 1996;275:224-9.

    • A confirmed case was laboratory confirmed or met the clinical case definition and was epidemiologically linked to a confirmed or probable case. A clinical case was defined as an illness characterized by a generalized rash lasting greater than or equal to 3 days; a temperature greater than or equal to 101 F (greater than or equal to 38.3 C); and cough, coryza, or conjunctivitis. A probable case met the clinical case definition, had noncontributory or no laboratory testing, and was not epidemiologically linked to a probable or confirmed case. ** A separate building with a small number of students.




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