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From July to September 2019, one cruise line, which CDC's report calls "cruise line X," had sudden outbreaks of acute gastroenteritis on 10 of its ships sailing in Europe, each sickening more than 3% of the passengers. The sudden vomiting and diarrhea, over within 24 hours, looked like norovirus. The cruise line investigated all summer and tested food extensively, but found no clear source.
Outbreaks reach U.S. waters
On September 18, 2019, CDC's Vessel Sanitation Program (VSP) was notified of an outbreak on the line's ship A, sailing from Germany to New York City. Ships carrying 13 or more passengers to the United States from a foreign port fall under U.S. jurisdiction. By the end of the 19-day voyage on September 23, 117 of 2,046 passengers (5.7%) and eight of 610 crew members (1.3%) met the case definition: three or more loose stools in 24 hours (or more than normal for the person), or vomiting plus another symptom such as fever, diarrhea, bloody stool, muscle aches, abdominal cramps or headache. Three of four stool samples tested at CDC's National Calicivirus Laboratory were positive for norovirus. A VSP team investigated on board on September 22 but could not find the source.
On October 7, VSP learned of two more outbreaks:
| Ship and voyage | Passengers ill | Crew ill |
|---|---|---|
| Ship B, to and from New York City along the East Coast | 85 of 2,166 (3.9%) | 10 of 612 (1.6%) |
| Ship A, Montreal to New York City | 83 of 2,251 (3.7%) | 10 of 610 (1.6%) |
The smoothie
VSP investigated ship B on October 12 and ship A on October 13. During those visits, the cruise line's public health officials reported that nearly 80% of food questionnaires completed by sick passengers on ship B named a smoothie made from frozen fruits and berries. Because berries had caused outbreaks before, CDC asked the Food and Drug Administration (FDA) to collect the frozen fruit and berries on ship B for norovirus testing. The lot numbers matched those of the same products on ship A.
The evidence
- Patients: nine of 11 stool samples from the three voyages were positive for norovirus, all typed as GII.2[P16]: three of four from ship A's first voyage, four of five from ship B and two of two from ship A's second voyage.
- Food: of 16 frozen fruit and berry items FDA tested, three carried norovirus: raspberries (genogroup II), a tropical fruit cocktail (genogroup I) and a berry mix (genogroup I).
- The match: norovirus sequences from the patients and from the raspberries were 97.5% similar.
Once the fruit was removed, the cruise line had no more outbreaks.
The source
Reviewing its supply chain, the cruise line found that from the end of June 2019 its food vendor had bought several containers, nearly 22,000 pounds, of frozen raspberries from a single lot from a supplier in China, and that they had gone to every ship in the fleet. Both the epidemiologic and the laboratory evidence pointed to the raspberries. On November 11 a recall notice was issued for frozen raspberries traced back to China; the report attributes it to the World Health Organization.
Why it matters
The investigation shows the value of watching for gastroenteritis at sea, both to stop illness from spreading through U.S. ports and to catch contaminated foods at sea before they have been linked to illness on land.
Sources
- Rispens JR, Freeland A, Wittry B, et al. "Notes from the Field: Multiple Cruise Ship Outbreaks of Norovirus Associated with Frozen Fruits and Berries — United States, 2019." MMWR 69(16). https://www.cdc.gov/mmwr/volumes/69/wr/mm6916a3.htm
- Recall notice as linked by the report: https://webgate.ec.europa.eu/rasff-window/portal/?event=notificationDetail&NOTIF_REFERENCE=2019.3843
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