Data | States which tested more in the initial days of the coronavirus outbreak found it easier to contain the spread

Data from Indian States and a town in Italy show that ramping up testing in the initial days helps flatten the COVID-19 curve

Updated - December 03, 2021 06:24 am IST

Published - May 05, 2020 12:45 am IST

A lorry driver being screened by a health-care worker at Inchivila on the Kerala-Tamil Nadu border on Monday.

A lorry driver being screened by a health-care worker at Inchivila on the Kerala-Tamil Nadu border on Monday.

How a region deals with the initial days of the COVID-19 outbreak determines its handling of the crisis.

Regions which ramped up testing in the first few days were able to flatten the curve early, while those which increased testing only later continued to record steep infection curves.

Lesson from Italy

A recent data blog published by the World Bank compares the case curve in the town of Vo in Italy (3,305 residents) with the case curve in the Diamond Princess cruise ship (3,711 travellers).

Vo tested almost all its residents after registering its first few cases, while the ship tested only those who showed symptoms. In the first round of testing, Vo detected more cases than the ship. In the second round, the number of new cases in Vo dropped.

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image/svg+xml*Infection rate per 100 people =(100 x total infected) / total populationParameterVoShipPopulation3,3053,711Cases (1sttest)8710Infection rate* (1sttest)2.60.3Cases (final test)6712Infection rate (final test)0.219.2

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In the ship, asymptomatic persons spread the infection to others causing a surge in cases in the second round of testing. Notably, while Vo initially quarantined only those who were infected, the ship quarantined most of its passengers.

Therefore, while lockdowns and quarantines help slow the spread, ramping up testing in the initial days flattens the curve.

How States tested

The chart plots the seven-day rolling average (median) of COVID-19 tests conducted per million population since the 10th case in select States where such data were available.

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image/svg+xml0510152025303540455055Days since the 1st case1251020501002005001,0002,000Median calc2000500100205101020304050BiharKeralaW.B.M.P.T.N.MaharashtraAvg. no. of tests per millionDays since the 10thcaseIn the first 24 days afteridentifying the initialinfections, Kerala's testrates were much higherthan othersWest Bengal's andBihar's responseswere poor initiallyand continue to be soTN had a sluggish start, but it recovered wellThough theyinitially respondedslower than Kerala,Tamil Nadu andMaharashtraramped up testingin the later days ofthe outbreak andeven surpassedKerala's test rate

Impact on case curve

The chart plots the infection rate per crore^ people for every 10 days since the 10th case. Kerala is the only State which recorded a drop in the infection rate. In most States, the infection rate is increasing in varying degrees.

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image/svg+xml50010020511 to 1011 to 2021 to 3031 to 4041 to 50BiharKeralaW.B.M.P.T.N.MaharashtraInfection rate per crore peopleDays since the 10thcaseDespiteMaharashtra'sand T.N.'s lateramping up oftests, infectionrates in theseStates continueto increase.This indicatesthe importanceof ramping uptesting in theinitial days ofthe outbreakInfection rates in Bihar and W.B. arestill low as these States continue toconduct fewer tests than other States

^Infection rate per crore = (1 crore x total infected) / total population

Source: World Bank, State health ministries.

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