A Hepatitis A Outbreak in the Marshall Islands, 2016–2017

In mid-September 2016, a case of hepatitis A was reported to the Marshall Islands Ministry of Health and Human Services. When laboratory tests confirmed four more on November 4, the ministry's Exposure Prevention Information Network (EPINet) team opened an outbreak investigation and asked the Pacific Island Health Officers' Association, the World Health Organization and CDC for help. CDC assisted remotely throughout, and its staff went to the islands in April 2017. Megan G. Hofmeister of CDC and colleagues reported the results.

The outbreak

Investigators interviewed patients in person and reviewed medical charts.

• A probable case: illness from September 1, 2016, with symptoms of acute viral hepatitis — such as fever, loss of appetite, nausea, vomiting, diarrhea, fatigue, dark urine, clay-colored stool or abdominal pain — plus jaundice or raised liver enzymes.
• A confirmed case: a probable case with a positive hepatitis A IgM antibody test or a link to a confirmed case.

From September 2016 to July 2017, 194 cases were reported: 168 confirmed and 26 probable.

Hepatitis A cases by week, September 2016–July 2017. Credit: CDC, MMWR.

Tracing contacts

Some contacts were found only after the recommended 14-day window for post-exposure vaccination had passed.

Stopping it

The EPINet team spread information on hygiene and vaccination through radio shows, mass text messages, posters and school talks, standardized case reporting and interviews, and widened case-finding through contacts.

Hepatitis A vaccine is not part of the Marshall Islands' routine childhood schedule. The response came in stages:

1. January 2017: vaccination of patients' contacts.
2. February 2017: a campaign for schoolchildren on Majuro, eventually reaching about 70% of kindergarten through eighth-grade students.
3. April 2017, once vaccine supplies were restocked: a second campaign for high school students aged 14–19 on Majuro.

In all, about 12,500 doses went to schoolchildren and to adult contacts. No new cases had been reported as of August 30, 2017. The original source of infection was never found; spread was mainly person to person.

A country in transition

The islands' previous hepatitis A outbreak was about 25 years earlier; since then, about five cases a year had been reported. Hepatitis A usually spreads by the fecal-oral route, through close contact or contaminated food or water.

The disease follows three patterns — high, intermediate and low endemicity — tied to hygiene and sanitation, clean drinking water, household crowding and socioeconomic conditions. As conditions improve, places move from high to intermediate endemicity, bringing more symptomatic illness and the potential for outbreaks. Hospitalizations and deaths rise too, as infection shifts from early childhood, when it is usually silent or mild, to adolescence and adulthood, when it is more often severe. The Marshall Islands had been thought of as a place where hepatitis A was constantly present; this outbreak suggests it may be moving toward intermediate levels. Health officials were weighing the costs and benefits of adding routine hepatitis A vaccination to prevent future outbreaks.

Sources

Based on Hofmeister MG, McCready JA, Link-Gelles R, et al., "Notes from the Field: Increase in Hepatitis A Virus Infections — Marshall Islands, 2016–2017," MMWR, Centers for Disease Control and Prevention; a work of the United States government in the public domain.