Estimating the risk of communicable diseases aboard cargo ships.

BACKGROUND

International travel and trade are known to be associated with the risk of spreading communicable diseases across borders. No international surveillance system for infectious diseases on ships exists. Outbreak reports and systematic studies mainly focus on disease activity on cruise ships. The study aims to assess the relevance of communicable disease occurrence on cargo ships.

METHODS

Retrospective analysis of all documented entries to 49 medical log books from seagoing cargo ships under German flag between 2000 and 2008. Incidence rates were calculated per 100 person-years at sea. Case series of acute respiratory illness, influenza-like illness, and infectious gastrointestinal illness affecting more than two persons within 1 successive week were classified as an outbreak. Attack rates were calculated based on number of entries to the medical log book in comparison to the average shipboard population during outbreak periods.

RESULTS

During more than 1.5 million person-days of observation, 21% of the visits to the ship's infirmary were due to presumably communicable diseases (45.8 consultations per 100 person-years). As many as 33.9 patients per 100 person-years sought medical attention for acute respiratory symptoms. Of the 68 outbreaks that met predefined criteria, 66 were caused by acute respiratory illness with a subset of 12 outbreaks caused by influenza-like illness. Attack rates ranged between 3 and 10 affected seafarers per ship (12.5&-41.6% of the crew). Two outbreaks of gastrointestinal illness were detected.

DISCUSSION

Respiratory illness is the most common cause of presumably communicable diseases aboard cargo ships and may cause outbreaks of considerable morbidity. Although the validity of the data is limited due to the use of nonprofessional diagnoses, missing or illegible entries, and restriction of the study population to German ships, the results provide guidance to ship owners and to Port Health Authorities to allocate resources and build capacities under International Health Regulations 2005.