Measles Imported by Returning U.S. Travelers Aged 6--23 Months, 2001--2011

Measles Imported by Returning U.S. Travelers Aged 6--23 Months, 2001--2011
Weekly
April 8, 2011 / 60(13);397-400




In the first 2 months of 2011, CDC received reports of seven imported measles cases among returning U.S. travelers aged 6--23 months; four required hospitalization. Young children are at greater risk for severe measles, death, or sequelae such as subacute sclerosing panencephalitis (1,2). Although all seven children had been eligible for vaccination before travel, none had received measles, mumps, and rubella (MMR) vaccine, the only measles-containing vaccine currently available in the United States. To characterize imported measles cases reported in the first 2 months of 2011 in U.S. travelers aged 6--23 months and compare them with cases in recent years, CDC analyzed data from the National Notifiable Diseases Surveillance System (NNDSS) for the period January 2001--February 2011. The results of that analysis indicated that, during January--February 2011, a total of 13 imported cases were reported in U.S. residents, including the seven children aged 6--23 months. During 2001--2010, a total of 159 imported cases were reported in U.S. residents, including 47 (range: 3--8 per year) in children aged 6--23 months (three of whom had been vaccinated before travel). Because measles remains endemic in much of the world, international travelers should be up-to-date on vaccinations. In accordance with the Advisory Committee for Immunization Practices (ACIP) recommendations, U.S. children who travel or live abroad should be vaccinated at an earlier age than those living in the United States because of the greater risk for exposure to measles outside the United States, and particularly outside the Americas (3).

In the United States, measles cases are reported to CDC by local and state health departments via NNDSS, using standard case definitions (4). Cases are classified epidemiologically according to the source of infection. An internationally imported measles case is defined as one resulting from exposure to measles virus outside the United States as evidenced by at least some of the exposure period (7--21 days before rash onset) occurring outside the United States and rash occurring within 21 days of entering the United States, with no known exposure to measles in the United States during that time. All other U.S. cases are considered U.S.-acquired. Laboratory confirmation of measles is made by detection in serum of measles-specific immunoglobulin M antibodies, isolation of measles virus, or detection of measles virus by nucleic acid amplification in an appropriate clinical specimen (e.g., nasopharyngeal/oropharyngeal swabs, nasal aspirates, throat washes, or urine). Monitoring of viral genotypes is an important component of measles surveillance and a tool to identify the likely source of imported viruses.

Imported Measles During January--February 2011

Of the 29 measles cases reported during January--February, 2011, a total of 28 were import-associated,* of which 16 (57%) were classified as imported cases; 13 of the imported cases (81%) were among U.S. residents. Of these 13 cases, seven (54%) occurred in children aged 6--23 months. All seven patients had recently traveled internationally; they were residents of Massachusetts (two patients), Texas (one), New York (one), Pennsylvania (one), Washington (one), and California (one). Median age was 10 months (range: 7--23 months) (Table).

Four of the seven patients were hospitalized for measles-related complications: two with diarrhea and dehydration, one with persistent fever, and one with pneumonia. The median duration of hospitalization was 3.5 days; all seven recovered. Diagnosis of measles was delayed in three of the seven patients. One was hospitalized for 3 days for pneumonia and "drug-induced rash," with a measles diagnosis made only after an unvaccinated sibling developed measles. A second patient visited a pediatrician three times before a diagnosis of measles was made in an emergency department and the child was hospitalized. A third patient did not receive an initial medical evaluation until 6 days after onset, and measles was not suspected until a follow-up visit 2 days later.

Measles was laboratory confirmed in patients 2--7 (Table). Although specimens were not obtained from patient 1, five siblings epidemiologically linked to this patient subsequently developed measles, and four of those cases were laboratory confirmed.

The seven patients had traveled to at least six different countries; two traveled to countries in the World Health Organization (WHO) Region of the Americas. Although patient 1 traveled to Haiti during the exposure period, an extensive investigation in Haiti found no evidence of measles transmission in that country. Further investigation identified another U.S. resident with onset of measles at about the same time as patient 1. This person had been in the same terminal of an international airport as patient 1 within a 2-hour interval suggesting a common exposure. For patient 3, an investigation conducted in the Dominican Republic identified as the likely source of this infection a European tourist with measles who stayed in a resort room adjacent to patient 3's family. The genotypes of virus isolated from patient 3 and patients linked epidemiologically to patient 1 all were D4 (Table), with genetic sequences closely related to those of viruses circulating in Europe. The genotypes detected in patients 2, 5, and 6 were the same as the genotypes associated with endemic transmission or recent outbreaks in the country of travel.

Imported Measles During 2001--2010

Of the 692 measles cases reported during 2001--2010, a total of 604 (87%) were import-associated. Of these, 292 cases (48%) were imported; 159 (54%) of the imported cases were in U.S. residents. Among the imports in U.S. residents, 47 (30%) were among children aged 6--23 months (range: 3--8 cases per year) (Figure). Among these 47 children, 23 were aged 6--11 months, 18 were aged 12--15 months, and six were aged 16--23 months. Although all 47 children had been eligible for MMR vaccination, only three (6%) had been vaccinated for measles before their departure. Fourteen (30%) of the 47 children were hospitalized; no deaths were reported.

Reported by
NM Cocoros, MPH, Massachusetts Dept of Public Health. J Zipprich, PhD, California Dept of Public Health. D Kuhles, MD, Nassau County Dept of Health; E Rausch-Phung, MD, CR Schulte, DS Blog, MD, New York State Dept of Health. P Lurie, MD, Pennsylvania Dept of Health. R Wiseman, MPH, Texas Dept of State Health Svcs. C Kroll MPH, Clark County Public Health; C DeBolt, MPH, Washington State Dept of Health. PK Kutty, MD,* SB Redd, AE Barskey, MPH, JS Rota, MPH, PA Rota, PhD, GL Armstrong, MD, WJ Bellini, PhD, KM Gallagher, DSc, Div of Viral Diseases, National Center for Immunization and Respiratory Diseases; AS Mahamud, MD, EIS Officer, CDC. *Corresponding contributor: Preeta Kutty, Div of Viral Diseases, National Center for Immunization and Respiratory Diseases, CDC, pkutty@cdc.gov.

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Measles Imported by Returning U.S. Travelers Aged 6--23 Months, 2001--2011