Covid-19 in Kerala: No justification for replacing TPR with WIPR as key metric

Rising number of cases of Covid-19 in Kerala
Kerala’s health minister Veena George. Large number of Covid-19 cases and the unfair criticism from within and outside seem to be forcing the state government take irrational pandemic management measures.

By CP Geevan

Covid-19 in Kerala: There are increasing worries about another wave of the pandemic. Of late, there has also been considerable attention on the testing numbers and test positivity rate (TPR) or the ratio of positive cases to total tests, usually expressed as a percentage. The TPR remained high throughout the second wave of Covid-19 in Kerala. Even long after it is believed to have peaked, the disease incidence has not shown any signs of going down. In parts of the state, it has been much higher than the state average.

The state has been targeted unfairly for the high disease prevalence despite the sero survey of ICMR showing that the proportion of individuals infected remains one of the lowest in the country and the case fatality rate (deaths to confirmed cases ratio) continues to be significantly low. The same central agencies that were blind to the unprecedented public health crisis in states like UP and Gujarat have been inspecting Kerala and giving all kinds of advice.

The opposition parties have also been sharpening their attacks on the state government over the large number of Covid-19 cases in Kerala. Incidentally, all states — be it Delhi, UP or Kerala — are supposedly following the national norms and protocols for pandemic containment, testing, and treatment. The states claim to have made only small changes and only within the margin allowed by the ICMR and Union health ministry.

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Kerala government under pressure

There seems to be no end to the cycles of lockdown and relaxation. Overall, there has been lock-down fatigue with livelihoods and businesses badly hit by the restrictions that show no signs of going away. Of late, discussions on Malayalam TV and social media show that under pressure, even the professionals involved in decision-making are becoming irrational. Around the world, testing is the bedrock of early detection of the trends in disease spread because epidemics like Covid-19 are highly infectious and the trends are exponential.

Ever since the high TPR in Kerala attracted excessive and unfair criticism, there has been a concerted effort within the state’s establishment to adopt other metrics. Many from even the Indian Medical Association in Kerala started to talk about an urgent need to replace tests-based metrics with those based on hospitalisation data. When it comes to defining what that would be, they have been unable to define it in a technically satisfactory manner.

In a recent newspaper article, one doctor argued that the rate of hospitalisation must be the key to decision-making. It is, indeed, an astonishing statement since every medical professional knows that is an approach rejected by experts globally because there is almost a lag of 10 days or more between date of getting infected and the hospitalisation.

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New metric to measure Covid-19 in Kerala

Apparently with the concurrence of the ICMR, another test-based metric, the Weekly Infections to Population Ratio (WIPR), has replaced TPR as the key matric for measuring the incidence of Covid-19 in Kerala. Its scientific basis is unclear. We cannot find any reference in scientific literature on the use of WIPR in epidemic management. It is difficult to understand the value of such an unproven measure. According to the Government of Kerala’s COVID-19 dashboard, WIPR is defined as: “the total number of Covid-19 infections reported in the week multiplied by 1000 divided by total population of the panchayat or urban ward.” The weekly infections reported should not be confused with 7-day running average.

The number of ‘weekly infections reported’ will depend on several factors, the most important being testing effort if it remains the backbone of disease monitoring. In WIPR, the infections detected or reported is not adjusted relative to the total number of tests carried out in the same period. That makes WIPR a metric devoid of the necessary attributes for comparison across locations, since testing effort and reporting vary considerably across locations.

The term reported introduces additional vagueness and a certain degree of informality. The term can mean cases detected from those having Covid-like symptoms or, it could be a combination of testing data from contact tracing and the cases registered at hospitals. Undoubtedly, such a measure cannot be a substitute for TPR which is adjusted for the testing effort. Using such measures can only make the disease management more difficult going forward.

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Covid-19 in Kerala: State must stick to proven metrics

There was never a good reason to blame TPR to begin with. The real problem with use of TPR has been the lack of consistency due to all kinds of variations in testing — methods (different types of tests; excessive use of Rapid Antigen Tests – RAT), testing effort (tests relative to population of the locality), and attempts to use unethical or unprofessional ways to somehow get a lower TPR. The antigen tests (detection of specific proteins on the virus surface) are not as sensitive as those based on molecular assays that detect viral RNA (e.g., the gold standard RT-PCR).

Due to lower sensitivity compared to PCR tests, the negative results (too many false negatives) from RAT must be confirmed with RT-PCR, which is rarely done in India, although ICMR recommends that. ICMR had promoted RAT because of its low cost compared to PCR tests. Society, however, must suffer greatly for excessive dependence on it.

The prolonged second wave of Covid-19 in Kerala combined with extended lockdowns and restrictions have led to a pandemic management fatigue. There seems to be a weakening of the excellent discipline that the local bodies and health professionals in the state showed during the first wave. In its place, the overriding concern now seems to be to find ways to lower the TPR. This must change.

Clearly, given the complexities of pandemic management, no single measure can be the sole determinant for key decisions. Metrics normalised to population of confirmed cases and adjusted to total tests conducted should be used. In addition, the vaccination coverage and reliable sero-prevalence data should be gathered and factored in. It is risky to underrate the significance and importance of testing effort and protocols. Only when same protocols are followed across the state, the indicators will have adequate consistency and integrity. That is necessary when the rule-based decision-making depend on those indicators.

Central agencies like ICMR must stop pointing fingers at Kerala with its excellent track record in public health, recognising that currently pandemic management and testing data are not comparable across the states. It is necessary to acknowledge that, in practice, the testing regimes vary considerably across states despite claims that each state is following the ICMR guidelines. Kerala must ignore the disconcerting attention it is getting and focus on following the global best practices instead of looking for quick fixes that carry the dangers of amplifying future risks.

Dr CP Geevan (Ph.D in Environmental Sciences, Jawaharlal Nehru University) is a Visiting Fellow, Centre for Socio-economic and Environmental Studies (CSES), Kochi, Kerala.)