Heightened fears surrounding COVID-19 have once again brought the idea of “patient zero” into public consciousness. Ever since it was coined by accident in the 1980s, this popular yet slippery term has regularly – and misguidedly – been applied to infectious disease outbreaks and public health efforts to control them.

Steve Wozniak, co-founder of Apple, tweeted earlier this month that he and his wife might be “patient zero” for the epidemic of COVID-19 in the US after they returned from a trip to China with symptoms. He later described his use of the phrase as “kind of a joke”.

Less frivolously, “the hunt for patient zero” formed part of a recent BMJ headline for an editorial examining the devastating epidemic unfolding in Italy. The piece described local attempts to find the country’s initial coronavirus cases, hypothesising that they might be a pair of visitors from China’s Wuhan region, where health authorities were confronting the world’s earliest recognised large-scale outbreak.

Amid heightened contact-tracing efforts to locate cases linked to a doctor in the UK who was displaying symptoms of the infection, the Daily Mail used similarly dramatic language. An article described “the desperate hunt … for an unknown coronavirus spreader” who “gave” – note the implied volition of this word – “the deadly illness to the UK’s 20th victim – the first Briton to catch it in the country”.

And even more recently, the Mail on Sunday followed news of prime minister Boris Johnson’s positive COVID-19 test result by publishing a two-page spread asking its readers: “DID BARNIER INFECT BOJO?” With little evidence, the authors intimated that Michel Barnier, the chief negotiator for the EU, “might be the ‘Patient Zero’ who brought [the] virus to No 10”, representing “the ultimate revenge for Brexit”.

With the words “patient zero”, you have a distinctly catchy phrase. This was the reason Randy Shilts, the American journalist whose work on the AIDS epidemic initially amplified the term, adopted it in the first place. It sounds scientific, and as if it signifies the absolute beginning of an epidemic. It shares a linguistic link to 20th-century military expressions such as “zero hour” (when an action begins) and “ground zero” (the point below where a bomb detonates), so it conveys a sense of excitement too.

But apart from its attention-grabbing tone, the phrase is hopelessly confusing. Its lack of precision and accidental formation disqualify it from formal usage, so most researchers will not touch it. And stories about unknown disease “spreaders” triggering a “desperate hunt”, whether or not they explicitly refer to a “patient zero”, are frequently giving expression to communal fears about dangerously reckless behaviour. On the surface, these stories seem motivated by science. Scratch a little deeper, though, and you will often uncover a desire to assign blame.

We should abandon the toxic phrase “patient zero” and discuss contact tracing – the process of locating individuals who have crossed paths with people who are infectious – with great care. Otherwise, we risk increased confusion, scapegoating and under-emphasising the significance of asymptomatic cases. These are all things which are deeply unhelpful for our collective response to COVID-19.

Confusion

First, let’s tackle the confusion raised by the term itself. “Patient zero” is often used interchangeably for three different scenarios: first case noticed, first case here, and first case ever. While there are legitimate reasons for discussing each of these situations, better terminology exists for doing so.

Speaking of “cases” instead of “patients” allows us to be more specific. By doing so we include those who may be infected and infectious but who don’t acquire official “patient” status by seeking treatment.

In terms of “first case noticed”, since at least the 1930s, health investigators engaging in contact-tracing work have used the phrase “index case” to mark the first person in a household or community whose symptoms grabbed their attention. Researchers studying tuberculosis in Tennessee during the Great Depression defined “index case” as “that person through whom attention was drawn to the household”.

Crucially, these same researchers were quick to emphasise that this person might not be “the initial case in the household in point of time”. Turning our thoughts to COVID-19, there are many reasons why this might hold true. An initial case whose symptoms were so mild that she did not seek assistance. A child who picked up the infection first but took longer than his siblings to develop a fever. Or perhaps a grandparent with all the signs of infection, but without medical insurance and afraid to seek treatment.

The Tennessee tuberculosis researchers also pointed out that the index case might not be a true case of disease at all. Someone might appear to be ill, draw attention to a household, but ultimately test negative for tuberculosis.

To refer to “the initial case … in point of time”, epidemiologists coined the phrase “primary case”. In understanding how a disease might spread through a household or community, it can be useful to know who was the primary case here, in a particular location. By knowing when this person was infectious and by tracing their movements through a community, investigators can identify other people who might be at risk of infection and, ideally, test and treat them.

Where epidemiology lacks a good alternative phrase is for the first person ever to become infected. “Patient zero” often springs up to fill this void in informal discussions.

There are many reasons why this person, the first human case ever in a particular outbreak, is seldom located: the absence of recognisable symptoms, gaps in disease surveillance, delays in recognising an outbreak, lack of effective testing. In some cases, the person popularly and arbitrarily crowned as “patient zero” may simply be the person with a positive test result whose likely date of infection is the earliest on record.

As such, any purported “first case ever” is largely figurative. Lacking a better phrase, we might choose to call this person the “alpha case” or “ur-case”, or, for infections such as HIV or COVID-19 where a virus transfers from an animal host to humans, the “crossover case”. “Crossover case” is readily understood. And “alpha” and “ur” are two words commonly used to describe absolute beginnings, each also hinting, appropriately, at a mythical realm (“In the beginning…”).

Each of these designations is meaningful. Index cases are helpful in terms of seeing how disease comes to authorities’ attention (“index” literally meaning “that which serves to point”). Primary cases are useful in terms of organising the key elements of epidemiology – time, place and person – into a narrative chronology that helps bring order to the complexity of rapidly accumulating data during a health crisis.

Likewise, it can be important to talk of crossover cases – even if they are seldom directly identifiable. Understanding their habits and living conditions might reveal risks that can be avoided in the future. Studying how a virus has evolved over time from its first interactions with humans can offer insight into its past trajectory as well as possible future points of intervention for treatment and vaccine research.

In short, each of these situations is worth discussing with precision. With its many possible meanings, “patient zero” is simply not up to the task.

Blame and scapegoating

Identifying a “patient zero” is also rife with potential to incite blame and scapegoating. To understand how, it’s useful to think historically about the overlapping but divergent interests of two different groups keenly following the spread of infection during an epidemic: members of the public and public health workers.

Long before they had the ability to test for specific germs, those studying epidemics – whether religious, civic or medical authorities – found value in locating the first cases. Like now, they were keen to work out what identifiable factors might have led to ill health in the community.

Many medieval Europeans believed that disease could spring up from dangerous miasmatic air. From the 14th century onward, conspiracies also circulated about specific minorities – lepers, Jews, heretics and sodomites – causing the plague, either directly by poisoning wells, or more generally by provoking God’s punishment with their behaviour. Members of minority groups who were judged to have disobeyed community standards often faced isolation, banishment and sometimes death in the aim of seeking atonement.

Humans are storytellers, and through several centuries of epidemics in Europe and North America (where my research has focused) they have told stories of how outbreaks started and spread. These included tales of how foreign travellers brought non-native disease (the malady from X country) – a phenomenon later aptly described in relation to AIDS as a “geography of blame”.

On a more local level, observers also described real and fictional chains of disease transmission between named people (“Our town was free from infection until so-and-so came”; or “A infected B with the pox, who infected C and D”). With their similarity to family trees, I call this second kind of story a “genealogy of blame”.