We need to test, trace, isolate -- there is no alternative
What my 14 years of working experience as a medical epidemiologist, including three years working as the lead field investigator for 30+ outbreak investigations in Bangladesh has taught me is that in the absence of an effective vaccine or therapeutics, “test, trace, and isolate” are proven public health control measures to curtail the transmission of directly transmitted emerging infectious disease outbreaks.
The theory is simple. Essentially what it means for the ongoing pandemic is that all symptomatic Covid-19 cases are promptly confirmed through laboratory testing, advised to isolate, and their contacts are traced and instructed to self- quarantine themselves. However, in reality the situation is far more complex.
Even countries with the best public health infrastructures have struggled to test, trace, isolate given the magnitude of the pandemic. For countries with diminished capacities, the situation remains far more challenging. Many countries have tried to adopt innovative approaches which can facilitate the implementation of these control measures, one such being the use of rapid antigen testing for prompt diagnosis of suspected Covid-19 cases.
The ongoing extensive community transmission of Covid-19 in Bangladesh has propelled debates, discussions, and controversies regarding the need for upscaling Covid-19 testing capacity. These discussions/debates are very valid given it has now been more than seven months of this pandemic and we all want some form of normalcy in our lives.
Much of these discussions have centred around replacing the gold standard RT-PCR test which is currently being used to confirm diagnosis of suspected Covid-19 cases with rapid antigen test. This makes complete sense if we consider the time gap between collection of respiratory sample for testing to making the test result available using RT-PCR technique.
In Bangladesh it generally takes two to five days, often more than three days.
I have already mentioned prompt testing is one of the key strategies to control infectious disease outbreaks. So why do we have to do prompt testing? We now know Covid-19 infection can start to spread from an infected person one to three days prior to onset of symptoms.
Additionally, people usually come for testing after they have had symptoms of Covid-19 infection for two to three days, which means by the time a suspected case comes for Covid-19 testing he/she might have been spreading the infection for three to six days unknowingly.
On top of that, if there is an additional delay of another three days before it can be confirmed whether a suspected person has Covid-19 infection using PCR test, then we have actually missed the opportunity to isolate the Covid-19 case when the person is most infectious. So, while RT-PCR test is the gold standard it is of little value in the absence of timeliness.
On the other hand, rapid antigen tests can give a “relatively” accurate result in a symptomatic person within 20-30 minutes, thus shortening the time lag by at least three days. They are also less expensive compared to RT-PCR. However, rapid antigen testing or PCR testing for that matter, is not the holy grail, it is just one component of the interlinked control measures of test, trace, and isolate. Rapid testing is a necessary but not a sufficient measure to control the pandemic.
The urgency of testing to confirm suspected cases of Covid-19 is not only to isolate the case but also to identify and quarantine contacts of the cases so that further transmission can be stopped. In the absence of proper isolation facilities and public health infrastructure to conduct effective contract tracing, neither RT-PCR nor rapid antigen tests will have any major impact on the infection curve of Covid-19.
While the director general of the World Health Organization Tedros Adhanom emphasizes that each member state should “do it all,” to expect that in Bangladesh -- a country of 160 million people with a population density over 1,200/sq-km and a fragile public health infrastructure -- even if testing was done rapidly, and contract tracing done effectively, is almost like finding a needle in a haystack.
Additionally, the vast majority of the people in Bangladesh are day labourers, without alternate financial stimuli to maintain livelihoods. Compliance to self-quarantine guidelines will always seem trivial. However, we must not give up, and we must continue to improve our capacity to test, trace, isolate not just for this pandemic, but for future events as well.
Lastly in our debates on whether rapid antigen test or RT-PCR test is the way forward for Bangladesh, we should not forget, there are other non-pharmaceutical public health interventions which are probably less complex. Regular hand-washing, covering our sneezes and coughs, isolating ourselves if we develop respiratory symptoms, wearing facemasks (correctly) when in public places, maintaining physical distancing as much as possible, and avoiding mass gatherings or events can limit transmission of Covid-19 infection.
Nusrat Homaira is a Senior Lecturer (Respiratory Epidemiology) at UNSW, Sydney, Australia.