The World Health Organisation director-general Tedros Adhanom has rightly stated that countries fighting the coronavirus should “test, test, test”.
Locally implemented, intensive community screening programs are crucial in understanding our risks during the COVID-19 pandemic. Massive testing campaigns are also the only way out to start easing the lockdown.
Massive screening programs in principle serve two purpose:
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.
**But why not screen everyone?
The average population of any district in India would be around 20-30 lakhs.
The problem of supply chain: 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 or around 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 (or a close to 3 month lockdown period) to test everyone who might be infected (assuming an infection rate of 1.0% in India).
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.
So who should these 1,50,000 people in a district be?**
Working with this constraint all questions can be converged to the one: "What convenience sample would provide an estimate of the infection spread in a district; were we to limit the sample size to screening 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. If we take the example of the district of Murshidabad, West Bengal; which is 9th most populous district in India with a population of 71,00,000 (as per 2011 district census) and average household size of 5.
Week1-3: Within the district we can start with villages/blocks/towns with more than 20,000 households. Murshidabad has 5 such villages with 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.
Week4: Health worker screening; we can assume infections in health workers and people conducting the screenings may have happened post the first few weeks. Murshidabad district has 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.
Week5: 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 screening of 'superspreaders' such as grocery shop owners; hawkers, police staff and household laborers. This will help us screen another 13,000 people.
Week6: We can move to screening the remaining 27 villages which are sparsely populated and screen grocery shop owners; hawkers priests and household laborers. This will require perhaps 500 screenings every village and we would have screened another 13,500 people.
The remaining 38,500 tests can be placed across primary health centers, fever clinics and hospitals for 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 at 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.
It should also be noted that community screening programs should involve people from local region and communities so that we can gain the trust of those who we intend to screen. Screening programs fail when people either don't cooperate during testing or do not comply to quarantine when found positive. It is therefore important that we let everyone know that the sooner we identify the disease; the less severe will be the impact and more likely they will be able to get proper medical attention. Personal health should be everyone's top priority at present!