OCTOBER 8 — The lay public is now much familiar with the Reproduction Number (Ro). More recently, with the explosive Covid-19 cases, the Ministry of Health did a modelling based on the Ro to predict the possible future outcomes.
The irony being, the coronavirus does not have a track record of behaving as an average pathogen in terms of its transmissibility. In other words, the Ro being an average measure of the bug’s contagiousness does not quite explain the phenomenon of clustering and super-spreading.
The index patient of the Hong Kong SARS-CoV-1 outbreak in 2003 epidemic was associated with at least 125 secondary cases, yet Ro of SARS-Cov-1 is three. The MERS-CoV outbreak in South Korea, the second largest outside the Middle East, can be traced to three infected individuals who caused 75 per cent of the total 166 cases.
A better explanation of this phenomenon is the dispersion factor k. Simply put, the SARS-CoV-2 like its predecessors, does not behave in a steady manner, instead infects in big bursts, where an infected person may spread to many persons all at once. It has been described as an over-dispersed virus which spreads in clusters.
Many reports in Asia testify to this fashion of Covid-19 transmission. In Indonesia, 80 per cent of transmissions were due to 10-15 per cent of infected persons. Hong Kong with its meticulous testing and contact tracing, reported that 19 per cent of cases were responsible for 80 per cent of transmission, while 69 per cent of cases did not infect another person. In South Korea, index patient number 31, generated 5,000 cases in a church cluster. A massive study from India, which looked at 85,000 cases and 600,000 contacts concluded that five per cent of cases was responsible for 80 per cent of transmissions. This jives very well with the 20/80 Pareto Principle whereby 20 per cent actions is responsible for 80 per cent of the outcomes.
We need to think beyond Ro and recognise that the majority of infected people barely spread it, but a few super-spreading persons and events caused most of the Covid-19 clusters.
And we similarly have a wealth of painful Covid-19 experiences in this respect. Early in the pandemic, the Jemaah Tabligh had their Ijtima’ (gathering) in Malaysia from February 28-March 1, 2020. It triggered the second wave of Covid-19 in Malaysia. It became the South-east Asia hotspot spreading to Brunei (50 cases), Cambodia (13 cases), Singapore (five cases) and Thailand (two cases). And 700 participants from Vietnam, the Philippines and Indonesia were investigated. The Tabligh cluster of 3,375 cases made up a quarter of the total Covid-19 cases in Malaysia. It contributed to 23 per cent of deaths and it spawned two sub-clusters causing 121 cases. It has spread deep into the community with five generations of spread.
Index patient number 26 spread the infection to 114 cases and the transmission has passed to four generations. Index case number 8937 in the Sivagangga Cluster super spread to 45 persons in Kedah, Perlis and Perlis and spawned three generations. The Tembok Cluster of prison inmates in Alor Setar, has now chalked 1,047 cases and has overtaken the Benteng Cluster in Lahad Datu.
Recognising over-dispersion, super-spreading and clustering as a key mode of transmission of Covid-19 would make us rethink a generic lockdown or MCO as the panacea to our present upsurge of cases. Unfortunately, this MCO-centric mindset has pervaded our thought processes and a point in case is the approach to the prison outbreaks and the imposition of targeted enforced MCO (TEMCO). Experts have called for the decongestion of the prison and offered ingenious ideas on decarceration. The prison ambience is the ideal environment for the interplay of the 3Cs of super-spreading namely close, crowded and confined. Within a space of 24 hours the Tembok Cluster in Alor Setar prison added another 394 cases (October 6, 2020).
Apart from prisons, hospitals, nursing homes, mosques, churches, mass transportation, enclosed offices, squatter housing and migrant worker dormitories are documented sites of super-spreader events.
We were doing very well and our numbers were in single digits until our politicians messed up our success story with the staged coup in Sabah and the inevitable re-elections. Politicians, their entourage, and the election campaigns are both super-spreader persons and events. Poor pandemic leadership, both civil and political, failed to proactively neutralise the potential hazards of this Covid-19 time-bomb which has now tipped the nation into a seemingly uncontrolled situation and a near-disaster.
No quarantine, no retesting, no tagging, and no tracking of returnees from Sabah, has imbued a false sense of security and has unleashed the third wave of Covid-19 with widespread community spread throughout the country. The “Menteri Cluster” has virtually confined the cabinet members to their homes not unlike the situation in the White House. It is utterly frustrating when the rakyat had been repeatedly told to follow the SOPs and who in the main complied, but the leaders who were not walking the talk were let off scot-free. And to add insult to injury, the political leaders in Sarawak had the audacity to call for state elections very soon in the future.
We should also be thinking differently on testing in our efforts to control and contain the outbreaks. There is a major reliance on rt-PCR as the assay of choice. And undoubtedly, rt-PCR is the gold standard for clinical diagnosis, and prior to instituting anti-viral and therapeutics. It therefore has High Analytic Sensitivity (HAS) to detect low viral load as found during the pre-infectious (early) and convalescence period. But it is expensive, limited to big laboratories and the turnaround time slow (TAT between one and four days). This High Analytic Sensitivity rt-PCR test cannot be frequently done because it is expensive and labour intensive and therefore it is a Low-Frequency Testing (LFT).
The Rapid Test Kit-Antigen (RTK-Ag) has a relatively lower RTK-Ag analytical sensitivity (85 per cent versus 95 per cent sensitivity of rt-PCR) but it has an accurate infection sensitivity. Therefore, RTK-Ag is an accurate assay for contagiousness which is key to stopping the transmission of infection with accurate diagnosis and immediate quarantine. For the purposes of surveillance, we need a paradigm shift from High Analytical Sensitivity and Low frequency Testing (eg rt-PCR) to Low Analytic Sensitivity and High-Frequency Testing (eg RTK-Ag).
RTK-Ag is probably 10 times cheaper than rt-PCR, it is much simpler and can be done at the Point Of Care. The turnaround time is rapid between 30-60 minutes. It can be repeatedly done and is a very powerful assay to utilise in mass, universal testing which would pick up asymptomatic cases, enhance tracking, ensure early isolation and quarantine, which would contribute towards a better and smarter strategy of cluster busting and the containment of Covid-19 whilst avoiding MCOs which hurts livelihoods and depresses the national economy.
* Dr Musa Mohd Nordin and Dr Husna Musa are paediatricians.
** This is the personal opinion of the writer or publication and does not necessarily represent the views of Malay Mail.