The best example of COVID-19 and its spread in a closed system with a relatively high degree of homogeneous population that I can think of is its spread among the aircraft carrier U.S.S. Roosevelt. All sailors can be classified as "susceptible" according to the SIRS modeling. Reasonable assumptions are that the sailors fall into age categories that are mostly under forty and very few if any are over sixty as well as that the sailors are fit with few if any chronic conditions. Mitigation measures such as social distancing could not be fully instituted until the ship docked with sailors working in confined areas for much of the time.
In a month, 100% of the sailors have been tested.
- the ship was at sea for fifteen days following their port visit before two sailors tested positive.
- the Navy concluded that this was evidence of pre-symptomatic transmission
- As noted in yesterday's post from retrospective studies, the mean incubation time (IT) was 5.5 days and 97.5% of people show symptoms within 11.5 days
- By April 16th, 655 had tested positive.. Two days earlier, Defense Secretary Mark Esper told reporters that only about 213 of the crew members showed any symptoms.
- That means only about a third of the 585 crew members who'd tested positive at the time were symptomatic.
- positive results for coronavirus have climbed to 840 by April 26th when all sailors on the aircraft carrier had been tested.
- Negative results amount to 4,098,according to the Navy.
- The Navy reported 4,234 sailors moved ashore into housing on Naval Base Guam and into hotels in Tamuning and Tumon.
- Sailors who test positive remain on base, according to Joint Region Marianas and Gov. Lou Leon Guerrero.
- Additionally, if sailors show symptoms while in hotels they are taken back to the base.
- Dozens of sailors who initially tested negative later tested positive.
- Of the total cases, 88 sailors have recovered, up from the 63 reported as of April 26th.
- As of April 27th, there were four sailors at the U.S. Naval Hospital and none in the ICU.
- Since the ship pulled into Guam on March 27, one sailor from the crew, Aviation Ordnanceman Chief Petty Officer Charles Robert Thacker, died after testing positive for the virus.
- Only sailors who test negative and who are asymptomatic are quarantined in Guam's hotels.
- Navy leadership is temporarily halting post-quarantine testing and is extending sailors' isolation more than three weeks after crew members continued to test positive for the coronavirus after a two week isolation.
Mortality rates for this group is easily calculated and, once the first cases were diagnosed, interactions with non-Navy personnel was minimized preventing contagion from new sources.
Coronavirus may spread faster than WHO estimate