Public health, private data

Like many Irish people, Mary Mallon took the opportunity to emigrate to the US to escape poverty and famine. Little did she realise that in the next couple of decades she was to become known throughout the country, even overseas. She soon started work doing the only task she really knew: cooking. But everywhere that she went, so people became ill. Between 1900 and 1907, she cooked for a total of eight families around New York City, seven of which succumbed to fevers and diarrhoea. Each time the family she worked for became ill, Mary Mallon moved on to work for someone new.

It wasn’t until early 1907 that Mary’s role in these outbreaks of typhoid was recognised, when the daughter of one of her employers died. George Soper, a sanitation engineer hired to investigate, managed to locate and identify her as carrying typhoid, and published his account in the Journal of the American Medical Association.

Mary Mallon refused to believe that she was the cause, and had to be arrested before it could be shown that her gallbladder was releasing large quantities of typhoid bacteria, which through faecal contamination of the food she cooked was giving her families typhoid. She was confined on North Brother Island for almost three years, until early 1910 when she made an undertaking to change her occupation, and was released.

After several years trying to work as a laundress, she returned to cooking under various assumed names. Wherever Mary worked, there’d be outbreaks of typhoid, and she moved on, until she started work at the Sloane Hospital for Women, where she infected 25 people of whom two died. She fled, but was arrested again and returned to North Brother Island. ‘Typhoid Mary’ finally died in 1938.

From the earliest cities in the Middle East, people have known about their risk of transmissible diseases, and over those millenia the discipline of Public Health has gradually emerged. From the pioneering work of the British physician John Snow to Typhoid Mary and more, Public Health has depended on the reporting of cases, tracing of contacts, and access to private and often very sensitive data.

Much of the world now faces a choice between three policies:

  • rigorous physical distancing to prevent person-to-person infection,
  • early reporting and thorough tracing of all contacts to isolate those who might become infected, or
  • let Covid-19 spread uncontrolled through the whole population.

Many of us have just spent the last couple of months or more experiencing the first of those. When there are high rates of infection, it’s usually the only effective solution, until rates of occurrence of new cases have fallen to a level where the second becomes practical. Then you need both distancing and contact tracing, but as fresh infections become rarer, distancing becomes decreasingly important.

Until the twenty-first century, no one seemed to have any problem with contact tracing. I recall it being performed to eradicate some of the last outbreaks of smallpox, for example. Because smallpox was highly infectious, with a R number of around 6-8 compared with Covid-19’s 3-4, and effective vaccination was readily available, cases would be identified early, and all their contacts traced, isolated and vaccinated – so-called ring vaccination. This last had to be done in Stockholm in 1963, and in Yugoslavia in 1972.

Now, fifty years later, our private data is too sensitive to allow us to report cases of Covid-19 early and trace contacts. People misleadingly refer to human contact tracing as track and trace to misinform others into thinking it’s about monitoring everyone’s location. We all wish that our local infection rates were the same as those of South Korea, except that we’re not prepared to let our governments have access to the bank card transaction (and other personal) data which that country uses to trace contacts.

An investigation performed by 9to5Mac in late May, just as Apple and Google were releasing their contact tracing support in iOS and Android, revealed how few US states were intending to introduce smartphone-based contact tracing: only 4 of 50 states contacted said that they would be using those facilities, and 17 including California said that they wouldn’t.

In the UK, trials of a separate app have lingered for the last month without any real progress being made. Yet last week, a national contact tracing service based on web and call centre interaction was launched. So far the heated debates on both have centred on the protection of private data, and how to prevent scammers from abusing the system. These are likely to actively discourage people from reporting Covid-19 infection, so defeating the whole system of contact tracing.

We love to blame our leaders and governments for what we, often rightly, consider their failings. So far we don’t seem to have shouldered much of the responsibility ourselves. It’s always someone else who has been breaking the rules, or the rules themselves were badly framed, or applied too late, or not applied properly. Since March, I have heard not a single person admit that anything they have done might have encouraged the spread of Covid-19. But I’ve heard an awful lot of excuses as to why people won’t engage fully with proven preventive measures such as contact tracing.

It’s our choice, but we all have to accept that the options are limited. Which will you go for: strict distancing, reporting and contact tracing, or uncontrolled spread? Remember that you may only get this choice once in your lifetime.


Mary Mallon on Wikipedia.
John Snow on Wikipedia.
Smallpox on Wikipedia.