Better hygiene and sanitation in the rich and developed countries could, paradoxically, be one of the reasons for the high rates of coronavirus-related deaths there, a new study by Indian scientists has indicated, lending credence to what is known as the ‘hygiene hypothesis’.
The study has tried to find possible explanations for the fact that lower-income countries, with higher population densities and much lower sanitation standards, seem to have recorded much lesser coronavirus-related deaths compared to richer, more developed, countries.
Shekhar Mande, director general, Council of Scientific and Industrial Research (CSIR), is one of its authors. Bithika Chatterjee of the Pune-based National Centre for Cell Sciences and Rajeeva Laxman Karandikar of Chennai Mathematical Institute are its co-authors.
The study is based on analysis of data until June 29, by which time more than 5 lakh deaths had been reported – more than 70 per cent of it in high-income countries.
In its endeavour to find a reasonable explanation for the counter-intuitive phenomenon, the study correlated coronavirus deaths in several countries with indicators such as GDP, population density, human development index rating, demography, sanitation and hygiene, and prevalence of autoimmune diseases. It found that ‘hygiene hypothesis’ could be one of the reasons for the dichotomy.
‘Hygiene hypothesis’ says that because people in countries with low sanitation standards get exposed to communicable diseases at an early age and develop stronger immunity, helping them to ward off diseases later in life, a phenomenon called ‘immune training’. Conversely, people in richer countries have better access to healthcare and vaccines, and things like clean drinking water, due to which they remain safer from such infectious diseases.
But that, paradoxically, also means their immune system remains unexposed to such dangers.
This hypothesis is also sometimes used to explain the prevalence of auto-immune diseases, in which the immune system sometimes ‘overreacts’ and starts attacking the body’s own cells, leading to disorders like type-1 diabetes mellitus or multiple sclerosis.
The study found that there was a stronger correlation of the coronavirus deaths with demography, sanitation, and prevalence of autoimmune diseases compared to developmental indicators such as GDP or HDI.
“Results of our analyses suggest that demography, improved sanitation and hygiene, and higher incidence of autoimmune disorders as the most plausible factors to explain higher death rates in richer countries. Thus, the much debated “hygiene hypothesis” appears to lend credence to the Case Fatality Rate dichotomy between the rich and the poor countries,” the study, published in ‘Current Science’, said.
Among countries with the highest rates of death per million of population are Belgium, Italy and Spain, where more than 1,200 deaths have died per million have been recorded till now. The US and the UK have more than 1,000 deaths per million of population.
In contrast, India has seen just about 110 deaths per million, less than half the world average of about 233. Most other South Asian countries, as also in rest of Asia and Africa, have much lower death rates.
It is not that there are no exceptions to this, as countries such as Japan, Finland, Norway, Monaco or Australia have also recorded very low death rates. But it is true that a majority of the deaths have occurred in the rich and developed world.
The study said: “One of the manifestations of better hygiene and safe sanitation practices in high GDP countries is the increased incidence in autoimmune disorders. It has been postulated that better hygiene practices could lower a person’s immunity and make the person susceptible to autoimmune diseases. We therefore tested if any of the autoimmune diseases showed an association with the LDM (log of deaths per million) variable. We interestingly find a strong positive correlation with Multiple Sclerosis, Type 1 Diabetes Mellitus, Rheumatoid Arthritis and Psoriasis and a weaker correlation with Asthma.
“Thus, our study seems to give empirical evidence supporting the ‘hygiene hypothesis ‘. It has not escaped out attention that there could be other factors such as the country’s stage of the epidemic and lower reporting/testing in less developed countries that could also affect the mortality numbers.”