Professor Virasakdi Chongsuvivatwong, or "Ajarn Vii" as he often calls himself, is the founder of the Epidemiology Unit and also an expert in infectious disease epidemiology and provider of insightful social commentaries during times of crisis. 

Over the past 2 months, Ajarn Vii has produced a series of reflective opinion essays (in Thai) on the evolving situation of the Covid-19 pandemic with a focus on the situation in Thailand, titled "Watching Covid-19 through the Eyes of an Epidemiologist". This article is the English translation of the Thai original.

The following essay was written on:

12 May 2020

Catch Me If You Can: Covid-19 Playing Hide-and-Seek in Wuhan

The original post in Thai can be found here

Wuhan City, Hubei Province, is an industrial city in the middle of China with a population of approximately 11 million - smaller than Bangkok. Since December 2019, Wuhan has become the epicenter of the Covid-19 outbreak. The Chinese government announced a shutdown and prevented movement into and out of the city since 23 January. When the situation stabilized and the last case was found on 8 April, or approximately 2.5 months later, the Chinese government began to allow people to do pubic activities. People came out to enjoy the late spring, right before summer started.

The day before yesterday, 10 May 2020, there were news of new cases in Wuhan. When the weather was comfortable at 22 degrees Celsius and 68% humidity, news reached Thailand that there were 6 new cases. The media reported that the government had ordered mass surveys - testing everyone in the city - to be completed within 10 days to eradicate Covid-19.

This news is very important in term of epidemiology. The first issue: is Wuhan's success in the first round facing vengeance from Covid-19 in this second round? The second issue: the Chinese government is engaging in the largest active case-finding effort in the world. Will this work?

I cannot predict either of these issues, but I will talk about them epidemiologically:

Outbreak data are like waves in the sea of time. What we are seeing right now likely began two weeks ago.  When we are infected with Covid-19, the virus incubates for about 1 week inside our body (may be shorter or longer - in some cases, the incubation period can be as long as two weeks) before symptoms present themselves. In the beginning, the patient may not believe that they are infected with Covid-19. Patients generally wait until the symptoms become more severe before seeking medical attention. Doctors diagnose and confirm Covid-19 by inserting a probe deep inside the nostril and sending the sample to the lab. Time is needed for testing and reporting. By the time the government makes the announcement and we know about it, two weeks have passed. We are chasing the shadow of Covid-19's past. We do not know what is happening at present.

A number of patients are pre-symptomatic carriers. When the pre-symptomatic phase is combined with the symptomatic phase, there are a number of days when the disease can spread. If the patient did not travel to see many persons, the spread of the virus would be limited. If not, the virus might have spread widely. If so, we might expect to see an increase in the number of new cases over the following days.

I believe that the success of the control of Covid-19 in Wuhan in this second round will not depend on the active case-finding, but on catching the infected people and isolating them in a timely manner. If the first spot is missed, Wuhan may break for the second time despite testing the masses.

I do not believe that mass testing will eradicate Covid-19. A certain group in the population have just been infected. They will not show symptoms, and tests will not detect the virus in their body. We call this a "False Negative".  For example, among immigrant workers who were smuggled into the country and detained in Sadao District, Songkhla Province, only 80% of the workers tested positive despite the group having lived together for months. Five workers tested negative. One week later, repeated tests were done and only 1 person tested positive. It was fortunate that the patients were in the holding cell, so the virus did not spread outside. But in open society outside of detention, False Negative test results will be a major problem in isolation of infected persons, particularly those without a history of close contact with a case.

After the first wave of mass tests, the False Negative cases will start to shed the virus, and Covid-19 likely will be happy and keep spreading. This game of hide-and-seek will continue. Each active case-finding effort is a big deal. If cases show up, whether to do active case-finding is something to be seriously considered.

In addition to the issue with False Negatives leading to the spread of the virus at a later time, False Positive results also create a problem. Among 11 million people living in Wuhan, there were not many infected people in this phase. The majority of positive test results turned out to be False Positives, which created many headaches in their own right. The same scenario happened when False Positive results were found in Yala Province last week.

We must pray for Wuhan to control the second wave of Covid-19 within days. If China is not safe, we will also suffer both in terms of the epidemic and the economy. We pray for Chinese epidemiologists to catch the infections tightly and early, and that there are no issues with active case-finding. Soon, in late July, it will be summer in Wuhan. This is one of the four muggiest cities in China in the summer. For those of you who believe that the virus does not spread in hot weather, please pray that the theory is true.

Looking at Thailand: we shut down our cities after Wuhan for a shorter period of time. We have not reopened travel to and from China. Unlike the last wave, this wave of infection will not yet reach us. We have similar lock-down measures as China, and we have experienced success similar to that of China. Now we are starting to reopen the cities, just like Wuhan. If our epidemiological model is also similar to Wuhan, soon we will experience the second wave of outbreak.

Contact tracing is an important tool in good disease control. The Thai public health system excels at this, but disease investigation will not be feasible nor effective if the outbreak is too large to control. The medical treatment system, the last line of the public health system, will also break. At last, we may need to revert to the old measures which no one wants: lock-downs.

Follow the news about Wuhan. Keep calm and help prevent the next wave of Covid-19 from happening in Thailand.

Composed by Prof. Virasakdi Chongsuvivatwong, MD, PhD. Epidemiology Unit, Faculty of Medicine, Prince of Songkla University.