The same week as Spain had its first day without a reported Covid-19 death, the San Francisco Bay Area had its first day since without a reported Covid-19 death since Covid-19 struck. I know how good that feels.
I’m a little concerned, though, when I see how crowded Dolores Park is during the George Floyd protests.
Those useful social distancing circles San Francisco created for Dolores Park a couple weeks ago are out the window.
Yesterday’s entry covered how we could avoid future Covid-19 outbreakes with vaccines and how we could mitigate the severity of future Covid-19 outbreaks with better treatments. Another aspect of Covid-19 management going forward is human behavior.
I mentioned the Pareto Principle a month ago in the context of herd immunity. Turns out there may be another Covid-19 application for the 80/20 rule: Covid-19 superspreadering. In a (not yet peer-reviewed) study of 1,038 cases in Hong Kong, researchers found the 80/20 rule applies to people who spread Covid-19.
Of the 349 local cases we identified — the remaining 689 cases were imported from other territories — 196 were linked to just six superspreading events. One person alone appears to have infected 73 individuals after frequenting several bars in late March. Weddings, temples, hot-pot dinners, work parties and karaoke venues featured in the other clusters.New York Times, “Just Stop the Superspreading,” 2 June 2020.
The study found that 20% of Covid-19 cases did most of the spreading while about 10% spread Covid-19 a little and 70% didn’t spread it at all.
Digging a little deeper, scientists characterize an epidemic’s transmission in two ways. One is the familiar reproduction rate, R. At any given time t during an epidemic, R(t) measures how many new cases result on average from each case at time t. At the beginning of an outbreak, t = 0. The basic reproduction rate R(0), or R naught, for Covid-19 is estimated to be between two and three. R goes up and down during an outbreak. One way or another, R always goes to zero at some point in time.
The other way scientists characterize transmission is in terms of its dispersion, k. Dispersion measures how many of the cases at time t generate new cases. In other words, if a lot of cases spread a disease, the disease is very dispersed. The Hong Kong study suggests that k = 0.45 for Covid-19. As my cool friends like to say, k is the new R.
The reason k is important going forward is that it tells scientists that some specific set of behaviors probably is responsible for most of Covid-19’s spread. If we can identify these, we can adapt to Covid-19 without treatments or a vaccine. This is what happened with condom use during the AIDS crisis.
New behaviors like wearing masks prevent Covid-19 from spreading. There may be more effective behavior modifications available. From what we know already, superspreading is probably some combination of the physiology or behavior of a person, certain types of events and locations, the kind of ventilation, the use of masks, and the duration and proximity of contact. It’s not clear yet how each of these factors contribute and whether there are other factors not yet discovered.
One thing on the mind of travelers is whether airplanes are implicated in superspreading. A recent Spanish flight to Canary Islands highlights why. Passengers were surprised to learn as the Spanish Civil Guard met their arriving flight at the gate that someone onboard had Covid-19.
The 53-year-old passenger had traveled to Madrid and then to Manzanares, in the Castilla-La Mancha region, to attend his mother’s funeral. Although the man had not been in contact with his mother, according to regional authorities from Castilla-La Mancha, he was in contact with the rest of the family, at least one of whom had tested positive for coronavirus. It was this diagnosis that prompted the man to get tested. Health officials realized the man was flying to Lanzarote when they tried to inform him of his test results.El País, “Outrage over passenger who boarded Spanish flight with coronavirus: “My son sat next to him”, 1 June 2020.
I was somewhat encouraged by the airline’s response. Iberia Express is providing free meals and health services to their passengers who are now in quarantine. Airlines trying to attract travelers need to manage passenger safety through the entire travel experience. For instance, if passengers can’t opt out of flights when they feel sick because of additional hotel fees or fees to change tickets, many will fly when they shouldn’t.
Parenthetically, Mom’s nursing home pays contractors to stay home if they feel ill in order to reduce the risk that sick staff members work when they need to pay their rent. Business needs to re-think sick time policies for the sake of not only the safety of their employees and vendors, but also their customers.
One thing people worry about on long airplane flights is ventilation. As in, how much Covid-19 is in the cabin air? Airline ventilation systems use a combination of fresh air and recycled air, recirculating the air inside the cabin every three minutes. Recycled air passes through HEPA filters to remove 99% of viruses.
HEPA filters are hospital-grade air filters, which means that they are the kind of filters used by hospitals to help insure that patients have the cleanest air possible. HEPA filters extract more than 99% of viruses – even those as small as 0.01 micrometers – so they can filter out coronaviruses specifically, which range from 0.08 to 0.16 micrometers in size.CheapAir.com, “How Airplane Ventilation Actually Works,” 14 March 2020.
What no one seems to know is how dangerous airplane cabins actually are. I can’t find any useful statistics, for instance, on airline crew Covid-19 cases or deaths. Even if the statistics exist, it’s difficult to tease out Covid-19 transmission that occurred in the air versus all the other places a crew member might contract the virus.
On April 28, a pilot reported sharing a hotel van with 18 other people, including the driver. Pilots were sitting shoulder-to-shoulder and most weren’t wearing masks.Bloomberg, “There’s No Escape From the Virus in a Cockpit at 30,000 Feet,” 7 May 2020.
On the science front, a new study from Germany finds two genetic loci associated with severely ill Covid-19 patients. In February, researchers collected blood from patients on ventilators in Italy. One similar genetic area they found among the DNA of these patients is involved with blood type. Chinese doctors noticed very early on that people with Type A blood are much more likely to have severe cases of Covid-19.
As scientists have begun to understand Covid-19 as a vascular disease in addition to or instead of a respiratory disease, I wonder if more connections to Covid-19 and blood related genes will be found. For instance, Covid-19 appears to be implicated in removing iron from red blood cells.
The other genetic area the German researchers found in common with the critically ill Italian patients is involved with both ACE-inhibitors and immune system signaling.
One of those gene candidates encodes a protein known to interact with ACE2, the cellular receptor needed by the coronavirus to enter host cells. But another gene nearby encodes a potent immune-signaling molecule. It is possible that this immune gene also triggers an overreaction that leads to respiratory failure.New York Times, “Genes May Leave Some People More Vulnerable to Severe Covid-19,” 3 June 2020.
Other researchers are looking at genetic links to Covid-19, too. This may help identify high risk patients or superspreading characteristics that, in turn, help mitigate future Covid-19 outbreaks.
Now that both Barcelona and the San Francisco Bay Area have had a day without a reported Covid-19 death this week, I’m turning my attention to Paris. My friend Anne wrote an up-close and personal account in Vogue about Paris opening up after its Covid-19 lockdown. Like Barcelona, Paris isn’t normal, but it’s sure better than March and April. Europe is opening up.