SYNOPSIS Epidemiology of Coronavirus Disease Outbreak among Crewmembers on Cruise Ship, Nagasaki City, Japan, April 2020 Haruka Maeda,1 Eiichiro Sando,1 Michiko Toizumi,1 Yuzo Arima,1 Tomoe Shimada, Takeshi Tanaka, Masato Tashiro, Ayumi Fujita, Katsunori Yanagihara, Hayato Takayama, Ikkoh Yasuda, Nobuyuki Kawachi, Yoshitaka Kohayagawa, Maiko Hasegawa, Katsuaki Motomura, Rie Fujita, Katsumi Nakata, Jiro Yasuda, Koichi Morita, Shigeru Kohno, Koichi Izumikawa, Motoi Suzuki,2 Konosuke Morimoto2 In April 2020, a coronavirus disease (COVID-19) out- by the World Health Organization on March 11, 2020. break occurred on the cruise ship Costa Atlantica in Na- COVID-19 also has been affecting global economies, gasaki, Japan. Our outbreak investigation included 623 leading to several recessions (2). Japan experienced multinational crewmembers onboard on April 20. Median an outbreak of COVID-19 on the cruise ship Diamond age was 31 years; 84% were men. Each crewmember Princess during the early stages of the epidemic in Feb- was isolated or quarantined in a single room inside the ruary 2020 (3–5). The government of Japan prohibited ship, and monitoring of health status was supported by entry into the country at the end of March, declaring a a remote health monitoring system. Crewmembers with state of emergency in 7 prefectures on April 7, which more severe illness were hospitalized. The investigation became a nationwide policy on April 16. Against this found that the outbreak started in late March and peaked in late April, resulting in 149 laboratory-confi rmed and 107 backdrop, the Italian cruise ship Costa Atlantica had probable cases of infection with severe acute respiratory remained docked at Nagasaki City since January 2020 syndrome coronavirus 2. Six case-patients were hospi- for full maintenance. In April 2020, we identifi ed an talized for COVID-19 pneumonia, including 1 in severe outbreak of COVID-19 on this cruise ship. condition and 2 who required oxygen administration, but COVID-19 spreads easily on cruise ships because no deaths occurred. Although the virus can spread rapidly of the “3 Cs”: crowded places, close-contact settings, on a cruise ship, we describe how prompt isolation and and confi ned and enclosed spaces (6–9). Given the spe- quarantine combined with a sensitive syndromic surveil- cialized setting of a cruise ship and its closed popula- lance system can control a COVID-19 outbreak. tion, a cruise ship can offer important insights about infectious disease epidemiology and transmission dy- evere acute respiratory syndrome coronavirus namics (10). How to manage an outbreak of COVID-19 2 (SARS-CoV-2) was fi rst reported from Wu- S on a cruise ship is a matter of debate, especially in a re- han, China (1), and led to outbreaks of coronavirus source-limited situation. To improve our understand- disease (COVID-19), which was declared a pandemic ing of COVID-19 and prepare for outbreaks to come, studies of outbreaks on cruise ships are valuable. In this Author affi liations: Nagasaki University, Nagasaki, Japan article we describe the epidemiology of the COVID-19 (H. Maeda, E. Sando, M. Toizumi, T. Tanaka, M. Tashiro, A. Fujita, outbreak on Costa Atlantica and approaches taken for K. Yanagihara, H. Takayama, I. Yasuda, N. Kawachi, J. Yasuda, managing and responding to this outbreak. K. Morita, S. Kohno, K. Izumikawa, K. Morimoto); Fukushima Medical University, Fukushima, Japan (E. Sando, I. Yasuda); Methods National Institute of Infectious Diseases, Tokyo, Japan (Y. Arima, T. Shimada, M. Suzuki); Disaster Medical Center of Japan, Tokyo Setting (Y. Kohayagawa); Nagasaki Prefecture Government, Nagasaki On April 19, 2020, offi cials of Costa Atlantica, which (M. Hasegawa, K. Nakata); Nagasaki City Public Health Center, had been docked in Nagasaki City since January Nagasaki (K. Motomura); Northern Nagasaki Public Health Center, Nagasaki (R. Fujita) 1These authors contributed equally to this article. DOI: https://doi.org/10.3201/eid2709.204596 2These authors were co–principal investigators. Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 27, No. 9, September 2021 2251 SYNOPSIS 2020, reported to Nagasaki City Public Health Cen- a risk factor for severe COVID-19, was defined as ter that they had febrile crewmembers (11,12). No a body mass index (BMI) >30 (14,15). Clinical signs passengers were on board the ship. All 623 crew- and symptoms of COVID-19 were fever (body tem- members had already completed their quarantine perature >37.5°C), cough, shortness of breath, nasal upon entry in Japan, but they had been asked to re- congestion, sore throat, nausea or vomiting, con- frain from leaving the ship unless necessary as part junctival congestion, headache, fatigue, myalgia or of the public health policy to prevent the spread of arthralgia, diarrhea, olfactory dysfunction, and taste COVID-19. Because of cruise ship employment con- disorder (loss of taste), which are globally recog- tracts, 56 crewmembers embarked during March 14– nized COVID-19 signs and symptoms (1,13,16–18). April 3. Given the COVID-19 pandemic, the body In managing this outbreak, the threshold value of a temperature of all crewmembers had been checked body temperature >37.1°C was applied on the basis daily since the end of February. Beginning March of the cruise ship’s definition for illness and criteria 22, at the discretion of the cruise ship company, any for isolation precaution. crewmember with a body temperature >37.1°C was We defined laboratory-confirmed cases as ill- to be isolated in a single-passenger cabin room of the ness in anyone with a positive test result for SARS- ship; beginning April 19, every nonessential worker CoV-2 by PCR or LAMP. We defined a probable was isolated or quarantined in a single-passenger case was defined as illness in anyone with signs or cabin room. Essential workers were defined as crew- symptoms indicative of COVID-19 but with a nega- members who were involved in the operation of the tive test result (19). We divided the severity of CO- ship or in maintaining its operation and functional- VID-19 into 4 groups (20): severe pneumonia that ity, such as the captain, engineers, and food prepara- required intubation or intensive care unit admis- tion staff. sion, moderate pneumonia that required oxygen On April 20, we performed PCR assays for SARS- administration, mild illness with COVID-19 signs CoV-2 for 4 crewmembers who had a body temper- or symptoms that did not require oxygen admin- ature >37.1°C, resulting in 1 positive result. During istration, and an asymptomatic condition without April 21–25, all crewmembers underwent universal any clinical signs or symptoms. We performed chest screening for infection by using loop-mediated iso- radiographs or chest computed tomography scans thermal amplification (LAMP) for SARS-CoV-2. After only for those suspected of having pneumonia, such the universal screening, each nonessential worker re- as prolonged fever or shortness of breath, and those mained isolated or quarantined in a single passenger who were hospitalized. cabin room. Even for those whose test results were positive, crewmembers with mild illness or without Testing Strategy signs or symptoms remained on the ship, and the We confirmed SARS-CoV-2 infection by using PCR or health status of all crewmembers was monitored dai- LAMP. We conducted PCR according to the protocol ly. If clinically indicated, regardless of test results, ill recommended by Japan’s National Institute of Infec- persons were transported and admitted to hospitals tious Diseases (21). LAMP is used for the detection of in Nagasaki City at the discretion of the ship’s medi- SARS-CoV-2 because of its fast turnaround time and cal doctor. acceptable levels of sensitivity and specificity (22–24). LAMP was conducted at the Institute of Tropical Data Collection and Definitions Medicine at Nagasaki University and Nagasaki Uni- The study population included 623 crewmembers versity Hospital. Persons who tested positive were al- who were on board on April 20, 2020. The cruise ship lowed to disembark and travel back to their countries company provided demographic and body tempera- after negative test results were confirmed in subse- ture data (ship’s medical record) during March 14– quent tests and their signs or symptoms had resolved. May 27 for all crewmembers on board. Demograph- ic data included sex, date of birth, nationality, and Data Analysis occupation category. Before disembarkation from We constructed an epidemic curve on the basis of the ship, crewmembers also provided information illness onset date, which was based on a body tem- regarding their smoking history, presence of any perature >37.1°C according to the ship’s medical underlying disease, height and weight, daily body record or the smartphone-based health monitoring temperature, and clinical signs or symptoms dur- system; the onset date of body temperature >37.1°C ing April 28–May 29 by using a smartphone-based was defined as the date when body temperature was remote health monitoring system (13). Obesity, as >37.1°C with a body temperature <37.1°C until the 2252 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 27, No. 9, September 2021 COVID-19 on Cruise Ship, Nagasaki, Japan, 2020 previous day. For the epidemic curve, we used body crewmembers. Of those, 25% (148/592) had a his- temperature >37.1°C for 2 reasons: first, it was the tory of smoking, and 3.7% (22/593) had underlying cruise ship’s definition for illness and criteria for diseases, including hypertension (2.0% [12/592]), di- isolation precaution; second, describing the epi- abetes (1.7% [10/592]), cardiovascular disease (0.2% demic curve based on the test results of SARS-CoV-2 [1/592]), and asthma (0.2% [1/592]). Median BMI from the universal screening would not give an ac- was 24.1 (IQR 21.7–26.7), and 9.4% (49/523) crew- curate picture of this outbreak because screening members had obesity (BMI >30).