6 Week COVID-19 Screening Strategy for Districts
#8 - Given a population of 1.3 Billion and limited testing capacity, we explore how to methodically go about screening high-risk individuals in a district.
“Test, Test, Test”
- Tedros Adhanom, Director-General of WHO
Locally implemented, intensive community screening programs are crucial in understanding our risks during the COVID-19 pandemic.
Mass screening campaigns will help end the lockdown.
They serve two purposes :
Preventing the spread of infection by identifying and isolating asymptomatic cases
Prioritizing care to members of the society who might be at high risk of morbidity.
Let’s start off by understanding why we are not in a position to screen everyone in the country.
Why not screen everyone?
The average population of any district in India would be around 20-30 lakhs.
With the current supply chain for rapid serological tests (and as per orders placed by ICMR), there can be a weekly supply of around 10,00,000 test kits per week (1,50,000 test kits per day) for the entire country. This averages to availability of merely 250 tests per day/per district.
This supply chain can test only 0.01% of the population and we would require 80 days (3-month lockdown) to test everyone who may be infected (assume 1% of population).
If we assume that by some stroke of luck the test kits manufacturing is ramped up to 10x. we will be able to do 2,500 tests per day/per district. In a period of two months (assuming transmission rates aren't increasing and there are no superspreader events), we should be able to screen 1,50,000 people in every district.
As you can see, not at all enough.
6 Week Screening Plan for Districts
Working with the above constraints, all questions can be converged to the one:
What sample would provide an estimate of the infection spread in a district, if we can only screen (test) 21,000 people every week?
This sample size would, unfortunately, depend on demographics of the district which varies greatly within India, so we can only speculate with examples here.
Take the district Murshidabad, West Bengal as an example. It is the 9th most populous district in India with a population of 71,00,000 (as per the 2011 district census) with an average household size of 5.
Week 1-3
Within the district, we can start with villages/blocks/towns with more than 20,000 households. Murshidabad has 5 such villages with an average number of households between 20,000-50,000. A minimum of 10,000 screenings should be performed in each of these villages, or two screenings for every 10th household. Since screenings are being done to identify 'spreaders', we can perhaps screen the working members of the family in the low-risk age demography. If found positive, the entire household should be placed in quarantine. We have now screened 50,000 people.
Week 4
Health worker screening; we can assume infections in health workers and people conducting the screenings may have happened after the first few weeks. Murshidabad district has a total of 3,500 ASHA workers and around 500 doctors. We can extrapolate this to an average health workforce (including ward boys, ambulance drivers, paramedical staff and hospital administration staff) of around 7,000 (this is an assumption). We should enable screening of the entire health workforce and their families which will amount to 35,000 tests.
Week 5
We can now move to villages/blocks with more than 3,000 households, Murshidabad has around 13 such villages/towns. As these towns are much less densely populated we can assume a lower transmission rate than more densely populated locales and an average of 1,000 people can be screened in these villages. These screenings can start with the screening of 'superspreaders' such as grocery shop owners; hawkers, police staff and household laborers. This will help us screen another 13,000 people.
Week 6
We can move to screen the remaining 27 villages which are sparsely populated and screen grocery shop owners; hawkers priests and household laborers. This will require perhaps 500 screenings in every village and we would have screened 13,500 people.
The remaining 38,500 tests can be placed across primary health centers, fever clinics and hospitals for the screening of symptomatic patients with complain of pneumonia. This can still help us handle a symptomatic patient load of 5,000 patients weekly.
This isn't a definitive approach and certainly can be looked further from other perspectives. The point however, is that for every district we need to calculate the maximum number of tests which can be made available over the next two months and then devise a testing ramp-up plan based on internal dynamics and demographic risks of the district.
Implementing an optimal screening strategy in such resource-constrained settings is a battle half won!
Our strategy for District Magistrates in India: COVID-19 is a war only Districts can fight.
We write from the India chapter of endcoronavirus.org! Our efforts were critical in the US in banning flights from China in Jan & other early outbreak control measures in India & the EU.
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