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Transmission trackers
Epidemiology is a word that’s been bandied about a lot during the Covid-19 pandemic. But what does an epidemiologist do, and how has gene technology been harnessed to help follow the trail of outbreaks?
Epidemiology – what is it ?
Rod Jackson is a professor of epidemiology in the School of Population Health at The University of Auckland; this means he knows a lot about epidemics, past and present.
“Epidemiology is the study of the frequency of disease across populations, and how to prevent and control those diseases,” explains Rod. "We infer cause and effect, through observation and prevention.
“Sometimes epidemiologists can prevent disease without knowing specifically what is causing it,” says Rod, who cites pioneering English doctor John Snow, whose removal of the handle from a London water pump, prevented further cholera infections in the community that used it. Despite not yet knowing that cholera was caused by a water-borne pathogen, the frequency of the disease in the local area and the common denominator of the water source, was enough of a smoking gun to make Dr Snow suspect the source.
As an epidemiologist, Rod is a doctor who became fascinated by the observation, analysis and application of health information. He heads a health data group that looks at risks and indications for cardiovascular health and disease. He is also a powerful voice in the reduction of Covid-19 transmission, and the vital importance to this of vaccination.
“Epidemiology is conceptually simple, but is very powerful,” says Rod. “It’s all about ‘the numerator over the denominator’, with the denominator being the population and the numerator being the people who are sick.” Within those numbers epidemiologists look for patterns and connections; learnings from these patterns are then used to inform decisions around the prevention and control of diseases both old and new – like Covid-19.
In the early days of the outbreak in Aotearoa New Zealand, epidemiology was applied to help predict case numbers and the future trajectory of the disease.
Gene technology was also extensively used to trace disease transmission between people. When the director general of health Dr Ashley Bloomfield announced daily how many cases were and were not ‘epidemiologically linked’, what he meant was how many dots could be easily joined between people to track the spread of Covid-19. Advances in gene technology have meant those dots can now be more easily connected, as a person’s specific viral infection can be genetically sequenced to help reveal who gave the virus to whom. From this, infection rates – or R-values – can help paint a picture of how many people are likely to be infected going forward. It’s a speculative but informed numbers game, based on knowledge of how epidemics have traveled in the past, and the influence of vaccines and other public health measures to reduce onward infections.
