key: cord-1001477-ol5xemfz
authors: MacIntyre, Chandini Raina
title: Case isolation, contact tracing, and physical distancing are pillars of COVID-19 pandemic control, not optional choices
date: 2020-06-16
journal: Lancet Infect Dis
DOI: 10.1016/s1473-3099(20)30512-0
sha: e9eacb3d406ec5b97f9b853148feb35cf0d38126
doc_id: 1001477
cord_uid: ol5xemfz

nan

Amid the urgency of the COVID-19 pandemic response, the study by Adam Kucharski and colleagues in The Lancet Infectious Diseases 1 reminds us that all available control measures should be used together to drive the effective reproduction number (R eff ) below 1. The word epidemic is widely misused, but true epidemic respiratory infections (when R >1) grow exponentially within days or weeks and thus we do not have time on our side. Delays or mistakes in disease control can be costly. Using UK contact data from 40 162 UK participants of the BBC Pandemic study and optimistic assumptions, Kucharski and colleagues modelled individual-level transmission during the COVID-19 pandemic stratified by setting (household, work, school, or other) with and without various non-pharmaceutical interventions (NPIs) including different testing, isolation, tracing, and physical distancing scenarios. Their findings showed that we do not have the luxury of picking and choosing between available NPIs to control COVID-19. A high proportion of cases need to be identified and isolated (in hospital or at home), with a high rate of contact tracing and quarantine along with physical distancing, to achieve and maintain epidemic control.

This finding might sound obvious, but on Feb 18, 2020, the eighth meeting of the Scientific Advisory Group for Emergencies in the UK concluded that "when there is sustained transmission in the UK, contact tracing will no longer be useful". 2 In Kucharski and colleagues' study, combinations of case isolation with contact tracing reduced transmission by 47% (self-isolation combined with app-based tracing) to 64% (self-isolation com bined with manual contact tracing of all contacts) compared with mass testing and case isolation alone, which reduced transmission by 2% (mass random testing of 5% of the population each week) to 37% (self-isolation plus household quarantine).

The COVID-19 pandemic is an unprecedented event in our lifetimes, and we have enjoyed the luxury of vaccines to control serious epidemic infections in the past century. As a result, we have rarely needed some of the other pillars of epidemic control on a mass scale. In the absence of a vaccine, control of COVID-19 relies on four main strategies. First, identifying new cases by surveillance and testing and isolating them to prevent further transmission. Second, tracking all contacts of cases and quarantining them for the incubation period, to reduce the risk of further transmission; quarantine is especially crucial for infections with asymptomatic or pre-symptomatic transmission, 3 and retrospective contact tracing to identify the source of infection of each case is also essential. Third, social distancing, ranging from spatial separation of 1-2m² to banning of mass gatherings and imposing lockdowns. And fourth, travel restrictions to stop the importation of infections. 5 Additionally, the use of face masks of even moderate effectiveness might help keep the R eff lower than 1. 6 The best available evidence suggests that masks are effective against beta coronaviruses in community settings and should be used in combination with physical distancing of at least 1 m. 4 Kucharski and colleagues showed that the first, second, and third strategies are not competing choices: none alone are enough, all are highly influential in epidemic control, and should be combined to bring R eff below 1. The lowest R eff in Kucharski and colleagues' study was achieved with a combination of case finding and isolation, contact tracing, quarantine, and social distancing (limiting outside contacts to four per day). For case finding, the authors showed that random testing (undertaken in some countries) barely reduced R eff and was not an efficient use of resources. Targeted testing of high-risk contacts in outbreak settings, regardless of symptoms, is much more efficient, especially given that asymptomatic infections are common. 7 Countries that are doing random testing but not testing asymptomatic contacts should review this strategy. For contact tracing, Kucharski and colleagues looked at manual contact tracing with selfisolation, which reduced transmission by 57%, and appbased tracing with 53% uptake, which improved that somewhat when in combination with manual tracing. However, the real value of app-based tracing is when case numbers are high and human resources stretched. Each case requires ten to 25 contacts to be traced, so the human resources requirement for manual tracing can easily be exceeded in a large epidemic. In that case, the use of an app might become essential for epidemic control. 8 Without contact tracing, isolation alone will not reduce R eff below 1 and will result in a blow-out of the epidemic.

The challenge of COVID-19, by contrast with severe acute respiratory syndrome, is that substantial transmission can occur in the absence of symptoms, 9 and accumulating evidence exists of aerosol transmission of the virus. 10 Although Kucharski and colleagues' study is specific for the UK, the findings are relevant to all countries. For countries that are opening up for business and resuming social activities, or where protests are occurring, as the number of social contacts increase, NPIs become even more crucial. It might even be worthwhile for countries to invest in strategies to vastly improve the uptake of contact-tracing apps to enable rapid response to resurgence of COVID-19. If you do not trace, you leave a chain of transmission free to grow undetected and exponentially. With 80% of cases being mild, it might take several generations of silent epidemic growth before a new outbreak is even recognised.

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Scientific Advisory Group for Emergencies. Addendum to the eighth SAGE meeting on Covid-19

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Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis

The effectiveness of full and partial travel bans against COVID-19 spread in Australia for travellers from China

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Comparative dynamic aerosol efficiencies of three emergent coronaviruses and the unusual persistence of SARS-CoV-2 in aerosol suspensions

The use of antibiotics anywhere could select antibiotic-resistant bacteria everywhere. Reducing the use of antibiotics in farm animals is consequently fundamental to preserve the current and future benefits of antibiotics for people. WHO ranks polymyxins among those anti biotics of the highest priority for reduction in animal use, given that they are of crucial importance to human medicine. 1 Therefore, the use of polymyxins (chiefly in the form of colistin sulfate premix) to treat and prevent infections and promote the growth of food-producing animals for decades is problematic, in view of their use in recent years to treat human infections caused by extensively drug-resistant Acinetobacter spp, Pseudomonas aeruginosa, and Enterobacterales. 2 Polymyxins bind to negatively charged phosphate moieties in the lipid A fraction of lipopolysaccharides present in the outer membrane of Gram-negative bacteria. As a result, the bacterial cell membrane is disrupted, leading to loss of intracellular products and bacterial death. Adaptive and acquired mechanisms of polymyxin resistance in bacteria culminate in charge modifications of lipid A. 3 For instance, alterations of the mgrB gene in the chromosome of carbapenemresistant Klebsiella pneumoniae (via mutations or insertion sequences) removes a negative feedback signal on the