New Paper Finds Startling Number Of Asymptomatic Covid-19 Carriers
by Alice G. Walton
Some of the most fascinating data in the Covid-19 pandemic have been produced by small, naturalistic experiments—from “sealed” environments (cruise ships) to subgroups of the population who had routine testing way before it was widely available (women checking into hospitals to give birth). These studies have shown lower death rates than previously thought and a relatively high rate of asymptomatic carriers.
The latest is another unwitting study, taking place on a small ship headed to the Antarctic Peninsula just as the pandemic was unfolding. Among the 217 passengers and crew were the three people who ended up writing the paper—clinician researchers from Australia, including lead author Alvin J. Ing of the Faculty of Medicine and Health Sciences at Macquarie University.
Here’s the short version of how the debacle unfolded (for a short podcast with Dr. Ing, see here). An avid photographer, Dr. Ing joined the expedition departing Argentina in mid-March, which was to retrace Ernest Shackleton’s 1915 voyage. As the WHO declared a global pandemic days before the departure, all passengers and crew were thoroughly checked for fever and overall health, and to make sure no one had traveled through high-risk countries recently. There was hand sanitizer and hand washing stations, but no social distancing procedures were implemented, making the ship a virtual breeding ground for a respiratory virus.
Everything was great for the first eight days, but on the eighth day, one person came down with a fever, at which point everyone quarantined in their rooms, and full measures to stop any further spread were implemented. Another 9 passengers or crew became symptomatic in the following 3-4 days. Since Argentina had shut down borders, the ship sailed to Uruguay, where it docked—by day 13, most of the fevers had improved. Rapid antibody testing was done on individuals who’d had fevers earlier, and all were negative (keep reading).
On day 14, three more people developed mild symptoms; of these, one was taken to a hospital for intubation on day 17. Seven others were evacuated to hospitals as well. One of these, the authors point out, was a 68-year old man who “developed fever on day 23 (15 days after cabin isolation) and was evacuated for hypoxaemia on day 24.” All evacuated patients tested positive with the gold standard 2019-nCoV RT-PCR test.
But here’s the really interesting part. On day 20, the Uruguayan health ministry provided all remaining passengers and crew with CDC’s 2019-nCoV Real-Time RT-PCR Diagnostic Panel.
- Of the total 217 passengers and crew on board, 128 (59%) tested positive.
- All of the people who’d tested negative with the Rapid test were positive with RT-PCR test.
- Of 128 people who tested positive, 104 (81%) were asymptomatic.
- Of the 24 who did have symptoms, 16 had fever and mild symptoms. (The other eight needed medical treatment (6.2%), including four needing intubation (3.1%). One person died (0.8%).)
Though it’s not totally clear how and whether the numbers may be applied to the general population, the small study seems to have some interesting takeaways. First, it confirms what others have suggested—that Covid-19 antibody tests probably don’t work well during acute infection. It also suggests that effective quarantine is difficult, and hardly foolproof even with physicians around. And of course, the asymptomatic rate is intriguing, and on par with other studies—it suggests that not only are there are considerable number of Covid-positive people without symptoms, but it may even be a majority.