Field briefing: Diamond Princess COVID-19 cases
Background:
[snipped some of the background summary] The Japanese government requested that the Diamond Princess stay at port, with no passengers or crew disembarking, in Yokohama when it arrived on [3 Feb 2020]. During [3-4 Feb 2020], the 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 Feb 2020], a lab-confirmed case of COVID-19 led to the quarantine of the Diamond Princess for 14 days beginning at 7 a.m., with passengers requested to stay in their cabins. As of [5 Feb 2020], 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 Feb 2020], passengers were provided thermometers for self-monitoring of body temperature, with instructions on calling a "fever call center" if they had a fever above 37.5 deg C [99.5 deg F]. 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 to 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 Feb 2020], 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 3711 passenger and crew aboard Diamond Princess on 5 Feb [2020].
Preliminary results:
[numbers snipped]
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 Feb 2020] (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 2020], 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 2020]. 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 [end of quarantine period] will be disembarked on [19 Feb 2020].
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.
[The source URL also has tables and graphs to support the conclusions presented above:
