Field Briefing: Diamond Princess COVID-19 Cases

Background:

A cruise ship, named the Diamond Princess, had travel that originated in Yokohama on 20 January and included stops in Japan (Kagoshima), Hong Kong, Vietnam, Taiwan and Japan (Okinawa), before arriving back in Yokohama on 3 February. During this time, a passenger who disembarked on 25 January in Hong Kong, has presented with cough since 19 23 Jan and was confirmed positive for Novel coronavirus on 1 February. The Japanese government requested that the Diamond Princess stay at port, with no passengers or crew disembarking, in Yokohama when it arrived on 3 February. During 3-4 February, health status of all passengers and crew members were checked by questionnaire by quarantine officers, and respiratory specimens were taken from symptomatic passengers, crew, and their close contacts to test for Novel coronavirus. On 5 February, a lab-confirmed case of COVID-19 led to the quarantine of the Diamond Princess for 14 days beginning at 7am, with passengers requested to stay in their cabins. As of 5 February, there was a total of 3711 individuals on board the Diamond Princess, with 2666 passengers and 1045 crew members.

Quarantine Measures:

At the beginning of the quarantine period, crew members were provided with personal protective equipment (PPE) and instructed on appropriate IPC practices. On 7 February, passengers were provided thermometers for self-monitoring of body temperature, with instructions on calling a “Fever Call Center”, if they had a fever above 37.5C. Passengers who developed fever were referred to the medical team in charge and were tested for Novel coronavirus. Passengers who developed serious illness, including non-COVID-19 morbidities, were referred the ship’s Medical Center, which provided essential health services. Those passengers with lab-confirmed COVID-19 were disembarked and transferred to an isolation ward at healthcare facilities. Their cabinmates were defined as “close contacts” and were therefore tested. If positive, they were also confirmed as a case and disembarked to a healthcare facility. If they tested negative, they remained on board but with a 14-day quarantine period reset after the last contact with the confirmed case. All crew and healthcare staff onboard the Diamond Princess were instructed to follow international guidance on infection prevention and control. To maintain operations of the ship, some crew continued to perform essential, limited services while the ship remained in quarantine. This led to those crew members not remaining fully isolated, in the same manner as passengers, during the quarantine period.

Data Collection:

Initially, only symptomatic cases and close contacts were being tested for COVID-19. This was changed on 11 February, due to the expansion of laboratory capacity, with quarantine officers systematically collecting respiratory specimens from all passengers by age group, starting with those 80 years old and older as well as individuals with co-morbidities, such as diabetes or a heart condition. Respiratory specimens collected were tested via PCR for confirmation of Novel coronavirus. Epidemiological data collected was initially limited due to the emergency nature of the quarantine and included data on onset of symptoms, date of lab confirmation, and close contacts. A confirmed case of COVID-19, for this report, is anyone, passenger or crew, who had a positive PCR test for Novel coronavirus, independent of their symptom presentation. In most cases, the “population on board,” refers to the 3,711 passenger and crew aboard Diamond Princess on 5 February.

Preliminary Results:

As of 18 February, there have been 531 confirmed cases (14.3% of all individuals on board on 5 February), including 65 crew and 466 passengers. A total 2404 respiratory specimens were tested, and 542 were positive (22.5), including double tests. Among confirmed COVID-19 cases with recorded symptom onset (n=184), there were 33 (18%) with onset dates before 6 February, which was the first full day of quarantine, and 151 (82%) with onset dates on or after the 6th. A total 255 (48%) of the confirmed cases were asymptomatic when the respiratory specimen was collected. Of these, 8 were crew and 247 were passengers. (Information on development of symptoms after disembarkation of asymptomatic confirmed cases is not currently available.) A total 23 passengers with reported onset dates were confirmed after another passenger in the same cabin had been confirmed. From 13 February to now, 81% of cases among confirmed passengers or crew with reported onset dates (n=22) occurred in crew (n=13) or passengers from cabins with a previously confirmed case (n=5).

Preliminary Conclusions:

Based on the number of confirmed cases by onset date, there is clear evidence that substantial transmission of COVID-19 had been occurring prior to implementation of quarantine on the Diamond Princess on 5 February (see also febrile patient visits to the on-board clinic below). The decline in the number of confirmed cases, based on reported onset dates, implies that the quarantine intervention was effective in reducing transmission among passengers. Transmission toward the end of the quarantine period, which is scheduled to end for most passengers on 19 Feb, appears to have occurred mostly among crew or within passenger cabins. It should be noted that due to the nature of the ship, individual isolation of all those aboard was not possible. Sharing of cabins was necessary, and some crew had to continue to perform essential duties for the functioning of the vessel with passengers aboard.

Recent confirmations of asymptomatic cases can be explained by the systematic testing of passengers that began around 14 Feb. Although some of these cases may have been secondary cases within a given cabin, it is difficult to know when transmission occurred. They may have been infected before the quarantine began. Nevertheless, these asymptomatic cases have been disembarked and their cabinmates have been defined as close contacts with their 14-day isolation reset on the day the asymptomatic case was disembarked. The systematic testing of asymptomatic cases was useful in screening these persons before allowing them to disembark.

Preliminary Actions/Guidance:

Those persons (mostly passengers) who have completed the 14-day quarantine, have not tested positive, and pass a medical check on the 14th day, will be disembarked on the 19th.

Those individuals who were in contact with a confirmed case will be put in isolation until they complete the 14-day period beginning after the last day of their suspected contact with a case. This includes a large proportion of the crew members of the Diamond Princess. The crew performed essential tasks that allowed the quarantine to occur successfully for 14 days and should be appreciated for their service.

As the persons aboard were exposed to a high-risk environment for a prolonged period, all persons who disembark should be careful about the health conditions for the time being and immediately report to a public health center if they develop symptoms.

Percent of persons aboard who were confirmed with COVID-19 by age group and symptom status at the time of specimen collection.

Age group Symptomatic confirmed cases (%) Asymptomatic confirmed cases (%) Total confirmed cases (%) Persons aboard on 5 February 00-09 0(0) 1(6) 1(6) 16 10-19 1(4) 1(4) 2(9) 23 20-29 18(5) 2(1) 20(6) 347 30-39 18(4) 5(1) 23(5) 429 40-49 18(5) 7(2) 25(8) 333 50-59 27(7) 22(6) 49(12) 398 60-69 73(8) 56(6) 129(14) 924 70-79 92(9) 136(13) 228(22) 1015 80-89 27(13) 25(12) 52(24) 215 90-99 2(18) 0(0) 2(18) 11 Total 276(7) 255(7) 531(14) 3711

Number of confirmed COVID-19 cases with reported onset dates, by onset date, aboard Diamond Princess, 6 – 17 February 2020 (n=151)

Febrile Patients, by date of clinic visit, Diamond Princess clinic, 19 Jan - 2 Feb 2020 (n=79)

Characteristics of COVID-19 Cases with reported on-set dates of 6 – 17 Feb 2020 (n=151)*.

Date of Onset (n cases) Crew Passengers Passengers from cabins with another confirmed case (%) 17 Feb (0) 0 0 0 16 Feb (0) 0 0 0 15 Feb (1) 1 0 0 14 Feb (5) 4 1 1 (100%) [0] 13 Feb (16) 8 8 4 (50%) [2] 12 Feb (12) 7 5 0 (00%) [2] 11 Feb (18) 7 11 3 (27%) [1] 10 Feb (10) 3 7 3 (43%) [1] 9 Feb (24) 5 19 6 (32%) [9] 8 Feb (18) 2 16 1 (6%) [3] 7 Feb (31) 2 29 4 (14%) [10] 6 Feb (16) 1 15 1 (7%) [6] Total 40 111 23 (21%) [34]

* The total number of cases in this table (n=151) is the total number of cases with known onset dates.

Note, the number in brackets represents the number of additional confirmed cases in the same cabin with unknown onset date.

Corrigendum: