Low diagnostic yield a threat to Health Workers? COVID-19 cases in Kenya 15th April 2020

Low diagnostic yield a threat to Health Workers? COVID-19 cases in Kenya 15th April 2020

The Ministry of Health announced another COVID-19 death today for a total of 10. The crude fatality rate is now 4.4%. As we are all aware, our health care system is relatively weak and we should expect that the mortality rate of COVID-19 patients with severe or even moderate disease will be relatively high. The total number of positive cases rose to 225 on the back of 9.620 tests done. The diagnostic yield reduced to 2.3%.

Implications of a Low Diagnostic Yield

The reason for testing for COVID-19 is to identify those who have the disease as early as possible so that the transmission rate can be reduced. It is important to remember that the test ‘looks back’ to confirm an event that happened on average about 5 days earlier, that is infection. Within 2 days of infection a person is shedding the virus and this can continue for for the duration of the infection. The situation gets complicated because 80% of persons infected do not have any symptoms, only 20% develop moderate to severe symptoms. So were it possible every susceptible person would be tested, that is mass testing.

Mass testing does not mean testing every single individual. It means testing all those who are susceptible as opposed to waiting to test those who present themselves with possible symptoms of the disease. The objective of mass testing is to buy time and establish the magnitude of the disease. How many have it? How many are spreading it? So that we can map out how much resource to put out in preparation for those who will present with moderate and severe disease. But there are some challenges that need to be overcome given our situation as a country. From the health system perspective.

The first problem is a health economics one. Testing for COVID-19 is not cheap. Because the disease is spreading right around the world there is no market price for the test. Countries are scrambling to get as many test kits as they can and universities, companies are scrambling to bring to use as quickly as possible new tests. Developed countries, having more money and having their own companies that can produce the test have an advantage in deploying the tests and being able to get better prices. Countries like Kenya, with no home grown industry are at a disadvantage and have to rely either on donations, international organisations like WHO and others to assist in procuring test kits. So the number of kits will be limited relative to the number of people who need testing.

The second problem is a laboratory science problem. The tests themselves are not 100% diagnostic of the disease. The main test being used Polymerase Chain Reaction (PCR) has diagnostic sensitivity of 67%. This means that it detects only two thirds of those with the disease. In this regard the test is similar to the rapid diagnostic test (RDT) used for malaria, where the lower the malaria prevalence the less accurate the test becomes. The test works best where there is a lot of disease. This has implications for COVID-19 because we know that the disease is highly infective. That means that if a person is tested early in the infection cycle, the PCR test may not pick up the disease, but may do so days later when the viral load is high. So a negative test, following some exposure requires repeat tests up to three times to be sure. This makes the test even more expensive as a screening test.

So Kenya like many African countries has a problem. In western countries, their social policies made it relatively easy to find susceptible populations. The elderly are bunched together in old peoples’ homes. It is estimated that up to 50% of the deaths in some countries have been residents of nursing homes. So mass testing in those countries involved testing such people and they were easy to find. The problem was that they were highly susceptible, many were not only elderly but have chronic conditions such as diabetes and hypertension. Then as they came in especially early on, they would also infection health workers some of whom also had chronic conditions.

So the challenge now for Kenya is to have a testing strategy that maps out the disease, giving enough time for the limited health system to get its’ act together. As cases pop up in diverse counties this becomes a difficult task. And it does not take much to paralyse a health facility.

Bandari Clinic, the in house clinic for Kenya Ports Authority was closed after seven positive cases and two deaths. We should expect to see more such occurrences, where just a few positive cases, not handled well shut down a health facility. Initially it might be possible to shunt a particular health facility’s patients elsewhere, but this cannot happen ad infinitum.

One solution to go in tandem with aggressive contact tracing and testing is to establish well equipped but relatively small health facilities, across the country – not another 1,000 bed behemoth that can be rendered useless in days. That would ensure that they can respond quicker to a cluster outbreak of COVID-19, but also if there is a problem then it is localised and health workers are protected to fight another day.

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Dr Richard Ayah

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