How lethal is Covid-19?

Coronavirus: Why death and mortality rates differ

Mostly, it's a story about apples and oranges.

And sometimes bananas and pears.

In Italy, an epicentre of the new coronavirus outbreak, the death rate at the end of March stood at a sobering 11%. 

Meanwhile in neighbouring Germany, the same virus led to fatality rates of just 1%. In China, it was 4%, while Israel had the lowest rate worldwide, at 0.35%.

. . . .

Several main factors account for much of the difference we’re seeing – and perhaps the most important come down to simply how we’re counting, as well as testing, cases.

First, there is confusion about what people mean by “death rate”. 

This confusion can make countries’ numbers look vastly different, even if their populations are dying at the same rate.

There are, in fact, two kinds of fatality rate. 

The first is the proportion of people who die who have tested positive for the disease. This is called the “case fatality rate”. 

The second kind is the proportion of people who die after having the infection overall; as many of these will never be picked up, this figure has to be an estimate. This is the “infection fatality rate”.

. . . .

So if some countries only test patients ill enough to go to hospital – and don’t test the less-ill (or even asymptomatic) Covid-19 patients who don’t get to hospital (which is what the UK is currently doing) – the death rate can appear higher than in countries where testing is widespread (such as Germany or South Korea).

. . . .

In fact, the lack of widespread, systematic testing in most countries is the main source of discrepancies in death rates internationally, says Dietrich Rothenbacher, director of the Institute of Epidemiology and Medical Biometry at the University of Ulm in Germany.

. . . .

There are other factors that alter the death rate, too.

One of them is what doctors actually count as a Covid-19 death.

. . . .

This is not necessarily a source of discrepancy between most countries, though, as many are counting deaths in the same way. Italy counts any death of a patient who has Covid-19 as a death caused by Covid-19; so does Germany and Hong Kong.

. . . .

While over-counting deaths among recorded Covid-19 cases may lead to overestimation of the death rate, there is another factor that could mean the death rate is also – confusingly – being underestimated at the same time.

This is the problem of hidden deaths from Covid-19: those people who die from the disease who are never tested. 

This comes into play when health services are overwhelmed and even those patients who have severe symptoms of the virus are not taken into hospital to be tested and treated, simply because there isn’t capacity.

In the small Italian town of Nembro, in Lombardy, only 31 people have officially died from Covid-19. 

But one preliminary study has found that it’s likely that far more people have died from Covid-19. 

That’s because the overall death rate – not just from Covid-19, but from all causes – was four times higher this year than in the same period last year. Ordinarily, around 35 people die in the first months of the year in Nembro. 

This year, 158 people were registered to have died.

This jump in excess deaths is speculated to be down to undiagnosed and untested cases of Covid-19.

. . . .

As well as differences caused by clinical definitions of what counts as a Covid-19 death and the numbers of people going untested, there are other factors that mean the virus hits some countries harder than others.

One that has been put forward by Italian doctors is the age profile of a country. 

In 2019, nearly a quarter of the Italian population was 65 years or older, compared to only 11% in China. 

The overall case fatality rate in Italy as of mid-March was 7.2% – much higher than China’s rate of 2.3% at a comparable stage of its epidemic. 

But from the ages of zero to 69, the two country’s case fatality rates are comparable, note researchers from the Istituto Superiore di Sanità in Rome.

. . . .

Heneghan suspects that one factor at play in Italy’s high figures could be not to do with the virus itself, but with bacteria. 

The country has the highest numbers of deaths due to antimicrobial resistance in the EU – in fact, a third of all EU deaths from antimicrobial resistance happen in Italy. 

While antibiotics do precisely nothing to tackle a virus, a viral infection can often open the way for secondary infections or complications like bacterial pneumonia. 

If that then can’t be treated properly with antibiotics because the bacteria is resistant, then this can be what kills the patient, not the virus itself.