The rise in travel-associated measles infections — GeoSentinel, 2015-2019

Measles remains a global threat to human health. In 2018, the World Health Organization (WHO) reported over 328,000 measles cases among 184 WHO member states, with the European Region reporting the most cases (25.6%) (1). From January to March 2019, reported cases rose 300% in comparison to the same months in 2018 (2). Low vaccination coverage for measles is presumed to be responsible for this recent increase (3–5). International travelers to measles-affected countries are at risk for infection and may contribute to disease importation (3, 4).

We examined records from GeoSentinel (www.istm.org/geosentinel), a global surveillance network of travel and tropical medicine providers that monitors travel-related morbidity, with a travel-associated confirmed (defined as a compatible clinical history plus viral isolation, nucleic acid testing, or seroconversion or rising titer on serology) or probable (defined as compatible clinical and exposure history plus a single positive IgM or an epidemiologic link to a known case) measles diagnosis from January 2015 through April 2019. Cases prior to 2015 have been reported previously (6).

Thirty-eight records (31 confirmed and 7 probable) were included, and the number of reported cases increased annually (Figure). Travelers were most frequently tourists (15; 39.5%) or visiting friends and relatives (11; 28.9%); 50.0% were female. Median travel duration was 14 days (range: 1–512 days). Median age was 32 years (range: 0–59 years); three travelers (7.9%) were less than a year old, five (13.2%) were 1–5 years, 24 (63.2%) were 20–40 years, and six (15.8%) were >40 years. Over two-thirds of 35 travelers (68.6%) with information available were hospitalized; 21 of 28 (75.0%) adults were hospitalized. Seven of 27 (26.0%) travelers with information available had a pre-travel consultation. Ten of 29 (34.5%) travelers with vaccination status reported were vaccinated against measles; the number of doses received was not reported. Travelers were exposed to measles in 25 countries: Indonesia (n=5), India (n=4), Venezuela (n=3), Brazil (n=2), Dominican Republic (n=2), Italy (n=2), Bangladesh, Colombia, Djibouti, Japan, Madagascar, Malaysia, Nepal, the Palestinian Territories, Poland, Republic of Korea, Romania, Saudi Arabia, Singapore, Somalia, South Africa, Sri Lanka, Thailand, United Kingdom, and Vietnam. One traveler who had been in India was also identified as potentially exposed on an international flight.

Figure.

Number of measles cases reported to GeoSentinel by year, 2015–2019 (n=36)

*Twenty-one GeoSentinel sites provided measles cases from 2015–2019; one site was added in 2016 (1 record reported in 2018) and two sites were added in 2017 (3 records reported in 2018).

Although GeoSentinel data are not representative of all travelers with measles, the number of hospitalizations, travel to countries with endemic transmission or known outbreaks, high median age, short travel duration, and low measles vaccination coverage among the travelers we describe are consistent with previous findings (5, 7). These data demonstrate that pediatric travelers are vulnerable to measles during travel, and highlight the severity of measles infection among adults (7), although this may be a reflection of a referral bias to GeoSentinel sites. The rise in global measles cases is reflected in these data, including measles acquisition in endemic and outbreak settings.

Unvaccinated and inadequately vaccinated travelers are at risk of acquiring measles (3). Travelers over 12 months old from the United States who do not have presumptive evidence of measles immunity should receive two doses of measles-containing vaccine at least 28 days apart; travelers 6–11 months should receive one dose, followed by a two-dose series given at 12–15 months and 4–6 years (7). Healthcare providers must avoid missed opportunities to promote adequate measles vaccination coverage, and develop strategies to promote vaccination (5) for children and adults.

*Members of the GeoSentinel Network who contributed cases: Carsten Schade Larsen and Christian Wejse (Aarhus, Denmark), Bram Goorhuis (Amsterdam, The Netherlands), Watcharapong Piyaphanee and Udomsak Silachamroon (Bangkok, Thailand), Susan Kuhn (Calgary, Canada), Cecilia Perret Perez and Thomas Weitzel (Santiago, Chile), Marc Mendelson and Salim Parker (Cape Town, South Africa), Nancy Piper-Jenks and Christine Kerr (Peekskill, New York), Tamar Lachish (Tel HaShomer, Israel), Prativa Pandey and Holly Murphy (Kathmandu, Nepal), Marta Menendez and Elena Esteban (Madrid, Spain), Karin Leder and Joe Torresi (Melbourne, Australia), Kunjana Mavunda (Miami, Florida), Camilla Rothe and Frank von Sonnenburg (Munich, Germany), Emilie Javelle (Marseille, France), Brian Ward (Montreal, Canada), Mogens Jensenius (Oslo, Norway), Eric Caumes (Paris, France), Poh Lian Lim (Singapore), Hedvig Glans (Stockholm, Sweden), Yukihiro Yoshimura and Natsuo Tachikawa (Yokohama, Japan).