CONTACT TRACING, UNIVERSAL TESTING, AND OTHER IMPERATIVES:

 

CONTACT TRACING, UNIVERSAL TESTING, AND OTHER IMPERATIVES:

--by Stewart Vriesinga

Contact tracing of positive COVID cases can be used to: 1.) Identify the person/situation in which a known positive case contracted the virus, and 2.) Identify the people and situations in which a positive case could have passed the disease on to others. Of these two objectives, without taking away from the importance of the latter, the former is probably the most useful in controlling the spread of the virus. It is also the most difficult. Why?

There is a considerable delay between when a person becomes infected and the relatively short period of time in which an infected person is capable of spreading the virus to others.

 

Here we see that the period of time in which an infected person is the most contagious begins two or three days before the onset of symptoms (if they develop symptoms at all), and for a few days after the onset of symptoms. However, contract tracing only intended to identify who a carrier may have infected is not enough. Furthermore, infected contacts will probably test negative for the first five days after transmission, so all contacts should self-isolate for five days before getting tested.

Contract tracing intended to identify where and from whom an infected person may have contracted the virus, though very difficult, is essential. Given that the incubation period –generally assumed to be as long as 14 days—the number of contacts from which an infected individual may have come into contact with is likely to be far more numerous than those to which they may have passed the virus. Contract tracing over this lengthier period of time (sometimes called backwards contact tracing) is the only way of determining where and from whom an individual may have contracted the virus. Eradicating the virus requires identifying the sources as well as those who may have become infected. We now know that much transmission occurs in outbreaks –so-called super-spreader events in which airborne aerosol (as opposed to the small droplets that fall to the ground within six feet) spread the virus to almost everyone who spends fifteen minutes or more in a crowded indoor gathering in a poorly ventilated social or work space. (Someone entering such a space even after it has been vacated can become infected by aerosol lingering in the air.) Backwards contact tracing –identifying the sources of transmission—help identify instances in which large groups of people may have become infected --large groups which may have remained undetected without backward contact tracing. Probable cases have to be identified, isolated, tested, and if needed, isolated. Transmissions that were not traced to their source –often to referred to by that ambiguous term “community spread”--result in any number of individuals continuing to spread the virus. To eradicate, or even curb the spread, all carriers --asymptomatic, presymptomatic and symptomatic—must be identified and isolated. 

The contact tracing necessary to do this requires an immense amount of resources. If the total number of cases are allowed to become too high, such contact tracing becomes all but impossible. That is where we are at now. Government measures to date have only sought to reduce the numbers enough to not overwhelm the healthcare system, rather than eradicate the virus or even reduce the numbers enough to allow for comprehensive contact tracing. When contacts are not identified, contacted and isolated within two or three days things spin out of control. They are now out of control. Even in-between the first, second, and third waves things were never really under control, because rather than allocating more resources to testing, laboratories, contact tracing, etc. governments chose to discourage those things in order to avoid overwhelming Public Health's existing capabilities. Only the prospect of overwhelming hospitals was enough to induce them to act, and then it was always too little too late. Hence we are in this endless ineffectual cycle of closures and reopenings.

There are better alternatives: We could have done, and still must do universal asymptomatic screening/testing in all workplaces, schools, etc.; Using the less invasive, less reliable, but more economical saliva tests, followed up with more reliable nasal swabs in the case of positive results; making much more use of economical waste-water testing, which, while it can't identify individual carriers, can provide entire communities with an early warning of any increase in the prevalence of the virus in their community, including among asymptomatic and presymptomatic community members, as well as identify which variants are present in a community. Waste-water testing has been used effectively for over a year now in some countries as well as some jurisdictions here in Canada.

Furthermore, given the evolution of new, more contagious, and deadlier variants, some of which are more resistant to current vaccines and infecting younger people; given that we don't yet know the efficacy of the vaccines currently in use at preventing infection and transmission (so far we only know that they're very effective at preventing disease and death after infection); given that the threat of COVID may be with us for a long time to come; for all these reasons it is essential that we put more effort and resources into eradicating and curbing the spread of this virus, rather than basing decisions on unsubstantiated, overly-optimistic presumptions that stop-gap measures will suffice until herd immunity sets in and everything goes back to normal through the use of vaccines. Because, however abhorrent it may seem, in all likelihood things will not go back to normal in the foreseeable future. The virus and its constantly evolving variants will always be one or two steps ahead of us. Viruses, which replicate by the billions on a daily basis, will not take billions of years to evolve, adjust, adapt to, and circumvent vaccines, even if if we are producing them in unprecedented record time.