9.8 SARS-CoV-2 and COVID-19

COVID-19 has a few notable differences when compared to SARS from 2003 - namely:

1. COVID-19 can cause mild illness and even death; it also has a higher asymptomatic rate than SARS

   Those without symptoms had similar levels of viral particles in their throats, though asymptomatic individuals tend to clear the virus faster and are infectious for a shorter amount of time.

2. COVID-19 patients can shed the virus before the onset of symptoms

   Peak viral shedding in SARS happens when patients becomes quite ill.

3. SARS-CoV-2 is more transmissable

   The virus can be spread by talking, sneezing, singing, and even shouting. SARS typically requires coughing, sneezing, and aerolization from medical interventions.

4. COVID-19 is not as lethal as SARS. COVID-19 alone killed more people than SARS and MERS combined even though its mortality rate is much lower.

5. COVID-19 is more widespread globally. SARS is generally restricted to a handful of countries in Asia.

9.8.1 Surveillance and risk assessments

There are four main ways we should test individuals:

1. A passive system via testing symptomatic individuals.
2. Active surveillance; we test individuals who do not display symptoms.
3. Seroprevalence - we try to understand the true infection rate in a population.
4. We can also monitor wastewater.

9.8.2 Wastewater for COVID-19 surveillance

Stool data from a study suggests “independent replication [of the virus] in the intestinal tract”. They also noted that while COVID-19 symptoms waned by the end of the first week, that viral RNA remained detectable in throat swabs well into the second week.

Figure 9.26: Amount of COVID-19 Virus Particles in Stool Samples

In the same study, the researchers found that stool samples remained RNA-positive for three weeks in six of nine patients in spite of them showing no symptoms. They also found that the viral load in stool samples were as high as those in sputum (i.e., phlegm) samples.

Consequently, this prolonged period of shedding provides a longer window of opportunity to detect an ongoing or recent infection.

The above is important as wastewater contains stool and respiratory discharges.

9.8.2.1 How do we implement wastewater testing?

There are three main parts:

1. Situation awareness

   A wide-area surveillance provides understanding of prevalences.

2. Cluster investigations

   These involve case investigations in high-risk clusters.

3. Dense living premises

   This can serve as an early warning tool against case identification and isolation.

   This can also expand to student hostels and nursing / welfare homes.

9.8.3 Confirmatory tests for positive COVID-19 results

Figure 9.27: A Confirmatory Test for Positive Results

The Orf1Ab gene can be amplified via PCR to be used for screening in all samples. Any positive samples after the latter can then be re-tested with a PCR that targets an alternative site (N1 in the figure)

9.8.4 Wide area surveillance in wastewater treatment plants

There is a very high correlation between the amount of virus in wastewater and the average number of cases across the country.

Figure 9.28: RNA Copies per Reported Case

The decreasing amount of RNA per reported case suggests that there is an increasing rate of detection of infections.

9.8.4.1 Surveillance at workers’ domitories

Figure 9.29: RNA Copies in Workers’ Dormitories Cases

The above supports the Joint Task Force’s domitory clearance strategy. It also supported the ACE in situation awareness in the domitories and complements swab testing, detection, and isolation.

Figure 9.30: Wastewater Signals at Workers’ Dormitories

A reduction in signals agree with individual swab tests results. The positive predictive value is 84.6% and the negative predictive value is 71.0%. Both values are thought to change with lower transmissions.