Measles Importation: Coming Soon to a Neighborhood Near You?
Abstracts & Commentary
By Frank J Bia, MD, MPH
Synopsis: No sooner had the CDC’s December 9, 2005 issue of Morbidity and Mortality Reports hit mailboxes and library shelves when New York City announced the arrival of a 12-month-old child at Kennedy Airport on December 17th with clinical measles. The numbers of acute measles cases in the United States may be reaching new lows, but the proportional contribution of imported measles, often in children who were traveling unprotected while visiting friends and relatives (VFRs), remains nearly 50%. The recent New York City experience highlights the issues which impinge directly upon those of us involved in the practice of Travel Medicine.
Sources: CDC. Measles—United States; 2004. MMWR Morb Mortal Wkly Rep. 2005;54:1229-1231; Gillian YA, Zucker JR. Imported Case of Measles on a Flight from Bangladesh. nyc.gov/health. 2005 Health Alert #48, December 29, 2005.
The Biman Bangladesh flight from Dhaka to JFK airport that arrived on December 17th was carrying a 12-month-old child with infectious measles. This young child from Queens county had not been vaccinated against measles prior to departure. Recall that travel recommendations for infants who are 6-12 months of age and are traveling to a measles endemic region call for measles vaccination. Patients who have measles are known to be infectious for 4 days before and after the onset of the rash. While in Bangladesh, she had been diagnosed clinically with measles on the basis of a rash with its onset on December 15th. Blood drawn on December 21st was serologically positive for both IgM and IgG antibodies. Virus isolations from urine and nasopharynx are still pending. Both parents and an older sibling had been vaccinated against measles.
The CDC report on measles in the United States for 2004 estimated the measles incidence level at less than one case per million population, and only 37 cases were reported for that year. This figure also represents a 16% decrease from the previously reported low of 44 cases in the year 2002. However, hidden in these relatively low incidence rates are important lessons for those of us who are travel medicine providers. Fully, 33 (89%) cases were importation-linked, and two-thirds of these could have been prevented if ACIP recommendations regarding measles vaccination of foreign travelers had been followed. Three states, Washington, California, and New York, accounted for nearly half the cases reported in 2004. Of these 37 cases, fully 27 (73%) were imported. These 27 imported cases were nearly equally split between foreign nationals traveling from abroad to the United States and US residents who acquired measles infection while traveling abroad (essentially, VFRs). The origins of these cases were skewed towards China (13), India (4), Bangladesh (2), and Thailand (2). Nearly half of the 27 cases were infectious during their airline flights. A single passenger who had been seated next to a person with infectious measles at the time was infected as a result of virus transmission during the flight, despite having a history of having previously received 2 doses of measles-containing vaccine at some point. The CDC had determined that all 14 US residents had been eligible for measles vaccination prior to exposure. In addition, of the 13 imported cases documented among non-US residents, 10 were unvaccinated and the other 3 had an unknown vaccination status.
There were 2 measles outbreaks in the United States during 2004. One represented imported cases from China among adoptees arriving in 3 states, and they resulted in one secondary case. In a second instance, a 19-year-old US student was infected in India, and his infection resulted in 2 secondary cases. One occurred in a patient who had been seated next to the student on an aircraft. Measles is highly infectious, and the potential for transmission on intercontinental flights would appear to be high. However, from 1996 to 2004, 117 patients with imported measles were deemed infectious during aircraft travel in which approximately 10,000 passengers were involved. Four secondary cases occurred and CDC investigators have speculated that the high level of immunity among largely adult passengers, perhaps coupled with vertical airflow patterns in aircraft, lowered the potential for secondary cases.
This is not the first time New York has dealt with imported measles from Bangladesh. In 2004, measles importation resulted in 2 outbreaks in Brooklyn and the Bronx. In Brooklyn, a 9-month-old girl returned from a 3-month trip to Bangladesh with diarrhea and fever. Several office and emergency room visits transpired until her rash appeared and she was diagnosed, during which time, 93 persons were exposed. A second case occurred in a 13-month-old who returned to the Bronx following a 3.5-month visit to Bangladesh. During 2 pediatric emergency department hospital visits, a total of 211 children were exposed to the index case.
The point is to underscore the potential for measles acquisition and spread as a result of importation, and much of that importation will occur as a result of unvaccinated children traveling to endemic areas. Infants who are between 6 and 12 months of age and traveling to endemic areas will not have been vaccinated at this point in their lives.
In general, adults born prior to 1957 are considered immune due to natural infection. They would not require vaccination for measles in preparation for travel. Vaccination is recommended for those adults who were born after 1956 and either were not immunized or received measles vaccines prior to 1980. Adults who have no history of measles diagnosed by a physician or no serological evidence of prior infection are also candidates for measles immunization. Pregnancy and immunocompromised states are relative contraindications to use of this live vaccine, but HIV-infected patients who are not severely compromised are at greater risk from measles than from the vaccine, so they should be considered candidates for immunization.
There is a possibility that children who are seen in travelers’ clinics, and are between the ages of 6 months and 12 months, could "fall between the cracks" and become the source of VFR-associated imported measles. Why? Children generally receive their first MMR (live measles, mumps and rubella vaccines) at age 12-15 months, and that is followed by a second dose, separated by at least 28 days. Usually the second dose is given at the time of school entry (age 4-6) or at age 11-12 if not previously administered.2 However, children between the ages of 6 and 11 months should be on an accelerated schedule for their measles vaccine, which is given in the following manner. They should receive a single dose of monovalent measles vaccine prior to departure for an endemic region, and pick up on the standard schedule when they return from their trip, or while abroad if the stay is an extended one. Often monovalent measles vaccine is not readily available, but MMR can be substituted. The unavailability of monovalent measles vaccine does not preclude measles vaccination for such infants.
- Zucker JR, Friedman S. 2004 Health Alert #6: Two Outbreaks of Measles in Brooklyn and the Bronx. nyc.gov/health March 16, 2004. Search Bangladesh for PDF file.
- American Academy of Pediatrics. Measles. In: Red Book 2003: The Report of the Committee on Infectious Diseases, 23rd ed, Pickering, LK (Ed), American Academy of Pediatrics, Elk Grove Village, IL, 2003, p. 419.