A Very Important Triangle

Countries where the Covid-19 epidemic hit hard are starting to ease their lockdown restrictions. Paradoxically, Cambodia, who has not really experienced the epidemic except by way of psychological and economic impact, continues to receive strong messages of “the second wave is coming” and “risk level for transmission is at an alarming rate”.

Until two days ago Cambodia had six weeks without a single reported case of Covid-19. The new case landed at Phnom Penh Airport and was almost immediately detected as positive to the virus. He has been admitted to hospital and the 63 passengers from his flight are all quarantined.

Six weeks without a case of reported Coronavirus and no reports of people dying from any mysterious respiratory illness is strong evidence, surely, that this virus is not going to impact Cambodia the way it has other places? When you study infectious diseases and epidemiology you learn about “the epidemiology triangle”. I’ve shared a copy below. Viruses don’t treat us all equally. Each virus has it’s own “preferences”, each host has it’s own characteristics that interact with those preferences, and it all happens in the context of different environments.

For example, when I suggest that tropical climates don’t seem to experience the same extremes of Covid-19 transmission, people have countered “what about Singapore”. There are only 5 million people in Singapore but they have had over 30,000 cases of Covid-19. Compared to Australia, with 25 million people and only 7,000 cases.

This argument ignores a number of factors:

  1. Australia’s tropical north appear to have had far fewer cases than our temperate southern regions (but the north is less populated so the rate of infection, rather than the number, is needed to analyse whether this is significant or not);
  2. Australia has had 101 Covid-19 related deaths in comparison to Singapore who have only had 23 deaths despite more than four times the number of cases. This allows a potential argument that tropical regions also have milder forms of disease?
  3. Singapore is a wealthy nation who lead a very urban and indoor lifestyle compared to Cambodia where 85% of people live in rural areas and 50% work in agriculture. Singapore is a hub of international travel whilst most Cambodians don’t see a foreign born person for years at a time.

Ultimately the epidemiological triangle can help to inform us of the mysteries we are seeing as different populations in different places experience this pandemic in very different ways. There are still many unknowns about this particular virus and its impact on societies. But is maintaining a sense of fear where all evidence suggests this virus is not going to take off, and where the population are being economically bankrupted, facing starvation and increased rates of other more significant and life threatening diseases, really the most practical response?

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