Throughout the course of the Covid-19 pandemic there has been the constant question of the risk of infecting other individuals after coming down with Covid-19. Is it a specific amount of time? There have been varying times used from >20 days to 14 days to 10 days to 5 days, and in some cases, requests that specific workers in healthcare return immediately even while actively infected with additional precautions including masks. Or perhaps there is a test that can be used? However the sensitivity of many of the popular antigen tests range is approximately 65-75% with a large margin for false-negative results. Conversely, PCR testing has very high sensitivity making it well equipped to detect the presence of viral RNA, yet can remain persistently positive in those who have been infected for weeks to months, far longer than the infectious period. Perhaps it is symptoms then? However, the symptoms of Covid vary to such a degree that many infectious individuals have no symptoms whereas others have severe symptoms requiring intubation even as they near the end of the infectious period. The approach that has been taken has been rational, generally well-conceived, even though many of the guidelines and regulations have been fairly criticized as a moving target throughout the course of the 2+ years of the pandemic.
The underlying principle to using any combination of the methods noted above is that some cutoff must be used whether it is the number of days, the often subjective sense of symptoms, or the sensitivity and negative predictive value of a specific test. And in choosing that cutoff a decision to allow for a certain tail, that is a certain number of outlying cases, must be made. In the distribution of cases, whether this is the cases fall within a normal distribution or another pattern, some distinction, a line in the sand, must be drawn separating the two groups. Although the actual status of infectivity is marked by varying shades of gray spanning the spectrum of white to black, practicality dictates a cutoff by which some amount of contrived yet agreed upon certainty is derived from amidst the uncertainty. By none of the above mechanisms or tests is there a way to guarantee with 100% certainly across a large population that a patient that has been diagnosed with Covid-19 is no longer infectious. In a small number of cases, often in patients with underlying diagnoses or complicating conditions, the infection may linger far longer than in the general host individual or may even reactivate in extremely rare cases at a later time if there is a significant immunocompromising factors or altered host anatomy or physiology. The only way to ensure that no infectious individual spreads Covid-19 is indefinite quarantine. Of course, this is untenable, unthinkable, and unpracticed for both the individuals as well as society at large. Instead a cutoff must be decided upon where the remaining infected tail of the population being studied is small enough to lead to an overall decline in infected cases while protecting the majority of the population and allowing society to continue to function with most individuals free to go about their lives after a brief hiatus for isolation and quarantine.
The current protocols in most areas of the country have sought to thread this fine line sometimes with outstanding results, in other cases with lax restrictions allowing rapid spread and overwhelming of the local medical establishment, and yet others strict enforcement causing undue quarantine and isolation with economic and social repercussions. No matter where this line is drawn, there will be a tail of people who are still infectious as well as people who quarantined for an extended time beyond their personal infectious period. There is no single right or wrong answer, rather there is a likely a range which individuals and society find generally acceptable. Critically, as the virus changes, as population density, vaccine and natural immunity rates vary, and as new data, testing, and treatment become available, this line should constantly be reevaluated. The place whether the line is drawn initially may continue to be reasonable and good, however there likely should be small, or even large, changes as this new information becomes available.
The problem of the tail is not limited to the current Covid-19 pandemic but has brought to light a problem that is faced with any disease and with any diagnostic test. Even beyond medicine, deciding where to draw the line, to designate a tail which is acceptable at the individual level, one must decide, for themselves what the acceptable level of risk is, as there is always risk. For every behavior from driving a car, to using a stove, to operating any appliance, to using money, to storing valuables, there is always a risk which is assumed as well as a benefit that is gained by interacting with the world and society at large. Specifically where to draw the line, where the acceptable tail of risk lies must be dynamically evaluated just as the situation, context, and technology dynamically change. Guidelines nor governments nor societies nor celebrity influencers can decide upon this cutoff in one’s stead. The hard work of constant consideration and reevaluation remains a personal privilege and even more, a personal responsibility. Constantly consider the tail.