Thailand is rapidly expanding testing for Covid-19. More importantly, the people in charge are working towards providing access to testing to all who need it. So far, the daily number of new cases is not increasing. This is encouraging, but may also give us a false sense of security. The public has for the most part accepted the necessity for restrictions on movement and economic activity, but some are already calling for relaxation of these essential control measures. But do we have enough information to make these decisions at the right time?
Are we missing something?
We know from other countries -- Japan, Italy and the United States -- that Covid-19 can circulate in a population for up to eight weeks with just a few cases daily, before erupting into a full-blown epidemic. During this pre-epidemic period, the small number of cases can provide the false sense of security that the situation is "under control". This can lead to complacency, decreased public cooperation and potentially to a premature relaxation of control measures.
What is the situation in Thailand now? Cases have been detected in 68 provinces. Cases which are not linked to any other known case and are not part of a cluster have been detected for several weeks, suggesting that the virus is circulating widely in communities. Case-contact investigations are difficult -- even the best investigations will miss some contacts who can go on to spread the virus. Infected individuals with mild symptoms are unlikely to visit health facilities but can spread the infection. Other barriers to seeking care -- fear of stigma, cultural or financial factors -- also contribute to under-reporting. At the other end of the spectrum, severely ill patients may be diagnosed with bacterial pneumonia and die without getting diagnosed with Covid-19.
What measures are in place now? Case-contact investigations, point of entry testing, and limited testing of symptomatic patients currently present at health facilities are all underway. But tracking the disease in individuals -- even large numbers of them -- is not the same as tracking the disease in the population.
What would a population-based testing strategy look like? This approach would seek out the virus rather than waiting for the virus to come to us.
While widespread testing of the Thai population in their homes and workplaces is not feasible due to financial and human resource limitations, systematic targeted surveillance, using a pooled specimen strategy and advanced testing technologies (RT-PCR) is realistic. In a pooled specimen strategy, samples can be pooled and tested together, then tested separately if the pooled sample is positive. This increases efficiency by reducing the total number of tests. RT-PCR tests detect viral genetic material, and are highly sensitive and specific for Covid-19 infection.
These methods could be applied to a systematic sample of patients with respiratory symptoms at selected "sentinel" hospitals in different regions on a scheduled basis. Post-mortem specimens from pneumonia deaths should also be tested to detect undiagnosed Covid-19 infections.
Regular surveillance testing should be done on systematic samples of health workers in hospitals and out-patient facilities, including individuals with no symptoms.
The key to this approach is regular (perhaps bi-weekly) systematic nationwide surveillance. If all of this information was collected and reported from "sentinel" facilities throughout the country, shifting patterns of infection would give us an early warning that Covid-19 in communities is heading in a dangerous direction.
With this information, supplies and human resources could be directed to developing hot spots before the situation veers out of control. It would also be possible to assess the impact of social distancing and other interventions and to make informed decisions on relaxing these measures.
In the absence of this information (and we do not have it now), we may face a sudden, explosive outbreak in Bangkok or elsewhere that would overwhelm our health system.
Thailand is respected around the globe for its public health system. It's time for a full-scale public health approach to Covid-19.
William L. Aldis (MD) is former World Health Organization Country Representative to Thailand.