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The Union health ministry on Sunday maintained that India has one of the lowest mortality rate (covid-19 case fatality rate). (PTI)
The Union health ministry on Sunday maintained that India has one of the lowest mortality rate (covid-19 case fatality rate). (PTI)

Variations in case fatality rates may be misleading

  • Difficult to compare nations; they may be less or more likely to report cases: WHO
  • Countries may be using different case definitions, testing strategies or counting differently

NEW DELHI : There are broad variations in estimations of case fatality rates (CFR) that may be misleading during the coronavirus pandemic, the World Health Organization (WHO) said in its latest “Scientific Brief".

This comes against the backdrop of the health ministry on Sunday maintaining that India has one of the lowest mortality rates (covid-19 case fatality rate) globally at 1.93%.

CFR is the percentage of people who die among all patients diagnosed with a disease, covid-19 in this case. Strictly speaking, though, it’s the proportion rather than rate, says WHO.

“USA crossed 50,000 deaths in 23 days, Brazil in 95 days and Mexico in 141 days. India took 156 days to reach this national figure," the ministry said.

Countries are difficult to compare for many reasons, one of which is that they may be more, or less, likely to detect and report all covid-19 deaths, WHO pointed out.

Graphic: Mint
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Graphic: Mint

“Countries may be using different case definitions and testing strategies or counting cases differently for example, with mild cases not being tested or counted," the WHO’s Scientific Brief said. Variations in CFR also may be explained in part by the way time lags are handled.

Differing quality of care or interventions being introduced at different stages of the illness also may play a role. Finally, the profile of patients, such as age, sex, ethnicity, and underlying comorbidities may vary between countries, WHO said.

This comes even as India’s toll reached 50,845 and the total tally of cases touched 2,634,256 on Sunday with more than 66,000 fresh covid-19 cases.

There are two measures used to assess the proportion of infected individuals with fatal outcomes, according to WHO. The first is the infection fatality ratio (IFR), which estimates the proportion of deaths among all infected individuals, including the asymptomatic. The second is CFR, which estimates the proportion of deaths among identified confirmed cases.

To measure IFR accurately, a complete picture of the number of infections of, and deaths caused by, the disease must be known. Consequently, at this early stage of the pandemic, most estimates of fatality ratios have been based on cases detected through surveillance and calculated using crude methods, giving rise to widely variable estimates of CFR by country, from less than 0.1% to more than 25%, WHO said.

WHO also released a document in the first week of August with formulas helping countries estimate CFR and, if possible, IFR, as appropriately and accurately as possible, while accounting for possible biases in their estimation.

For covid-19, as for many infectious diseases, the true level of transmission is frequently underestimated because a substantial proportion of people with the infection are undetected either because they are either asymptomatic or have only mild symptoms and thus typically do not approach healthcare facilities, WHO said. There may also be neglected or under-served segments of the population who are less likely to access healthcare or testing. The Union government has recently admitted to the facts that WHO has highlighted in the scientific brief in bias and underestimation of the CFR such as delays in reporting deaths. Before the Union health ministry recommended a uniform standard to declare deaths, states were using their own norms to count covid-19 deaths.

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