By Henry I. Miller and Andrew Fillat
Every day seems to bring some new, unexpected, unpleasant revelation about the SARS-CoV-2 and the illness it causes, COVID-19.
The infection has a long, often asymptomatic incubation period, high transmissibility, the ability to infect many human tissues, and, frequently, rapid deterioration of the clinical course. Some curious aspects of the infection, such as long duration of symptoms, multi-organ involvement, blood clots, and patients’ ability to tolerate extremely low blood oxygen levels have put critical care doctors on a steep learning curve, trying to understand how best to keep patients from falling off a cliff.
If the clinical aspects of the disease have been difficult to catalog and manage, the public health considerations have been equally vexing. We know enough now, however, to offer improved guidance for setting public health policy. Rather than using projections of cases and fatalities to guide policy decisions, the focus should be on the granular level of how the virus physically spreads. It is time to relegate the COVID-19 epidemiological models primarily to projecting required hospital and ventilator capacity and supplies of personal protective equipment.
Based on a survey recently in New York, it appears that a very high percentage of new cases can be traced to individuals’ homes and to care facilities such as nursing homes. The survey found that 83 percent of new cases came from unemployed or retired individuals who are largely sheltered in place, while almost a quarter (22 percent) of these cases originated in long term care facilities. In the nation overall, 11 percent of COVID-19 cases have occurred in long-term care facilities, while deaths from the infection in long-term care facilities account for more than one-third of the country’s pandemic fatalities.
We are also learning more about the role of children in spreading COVID-19 from an analysis just released by the Netherlands’s National Institute for Public Health and the Environment:
Worldwide, relatively few children have been reported with COVID-19. Data from the Netherlands also confirms the current understanding: that children play a minor role in the spread of the novel coronavirus. The virus is mainly spread between adults and from adult family members to children. The spread of the virus among children or from children to adults is less common.
With sufficient resources, there are measures available to mitigate institutional spread that must be more widely and aggressively applied. There are limited controls available within households, however, so the main objective there needs to be eliminating the introduction of infection and performing contact tracing once that bubble has been pierced.
Those findings are consistent with an excellent article by University of Massachusetts immunologist Erin Bromage that explores the math of virus transmission. It strongly suggests that most forms of short-lived, non-intimate contact have little chance of transmitting a sufficient load of the virus to infect anyone except the immunologically compromised. Outdoors, the probability becomes even lower, because of air movement and dilution, and the consequent dissipation of viral particles. In short, the science suggests that outdoor activities with prudent distancing pose very low risk.
The same analysis shows that in indoor environments, the key physical factors are the rate of air exchange and the overall volume of air in the space. So, for example, a big-box store with effective air conditioning (ideally, with HEPA filters) is far less favorable to transmission than, say, a small boutique. This also explains why crowded restaurants and bars and homes and non-hospital care facilities are so conducive to contagion.
The second critical consideration is the number and distribution of virus particles emanating from a person who is infected. A cough projects far more virus a greater distance than breathing, and a sneeze is still worse. At least 44 percent of all infections are transmitted by people without any symptoms (asymptomatic or pre-symptomatic people), who can be shedding the virus into the environment for up to five days before symptoms begin.
Although no prescription for behavior can be perfect, we can offer some guidance.
First and foremost, people with known exposure to COVID-19 or with fever and cough or sneezing should not go out in public, and should wear a mask if they must leave isolation. (If there were to be any basis for strict enforcement, we believe this should be it.) They must isolate as much as possible, preferably somewhere with effective air exchange and filtering to avoid infecting family and anyone else in close proximity.
Along similar lines, indoor capacity controls should be tailored to the type of space and efficiency of ventilation. Roping off sections of a big box store is senseless, compared to overall capacity management and requiring that staff and customers wear masks. One logical government program might be to subsidize the installation of HEPA filtering and HVAC systems that can move greater volumes of air.
Because infections will still occur, contact tracing becomes very important. A high priority should be placed on testing of households where infections may have spread before the onset of symptoms in the first case.
Although we know that pre-symptomatic people can spread the virus, it is less clear how capable of spreading infection are individuals who are known to have been infected but remained asymptomatic. For that reason, it is critical to continue extensive population screening with accurate (validated) antibody tests, in order to assess the magnitude and importance of asymptomatic infection.
Taken together, these considerations suggest logical guidelines. It is clearly past time to rein in the baseless, arbitrary restrictions that have been imposed by some politicians, as they can only inspire non-compliance and contempt. Predicating policy on transmission dynamics can clear away the miasma of regulation based on macro trends and guesswork. We still need continued research on how the SARS-CoV-2 virus can most effectively be prevented from spreading from person to person.
Social distancing, testing, and the wearing of masks in relevant settings should be continued, along with contact tracing. The improvement of HVAC systems is less obvious, but also critical. Keeping the most dangerous—i.e., potentially most prolific—sources of spread contained should be the focus of enforcement.