More information about text formats
We read with interest your Editorial on Global health and human rights for a postpandemic world and offering our comments on this important issue.1
COVID 19 has rampaged an unprepared world. With its high infectiousness, low virulence and asymptomatic transmission, it has crossed boundaries rapidly and affected millions. The mode of transmission of the disease, whether by large droplet (>5µm) as fomites through surface, short distance aerosol borne or long distance airborne by small particles (<5µm) is still being debated Containment and lock down strategies adopted by all affected countries to control the spread have shown mixed results but has devastated the economy and caused major societal disruptions. The policy makers aggressively contained densely populated urban areas, quarantined ships, care homes and jails but the disease has continued to spread rapidly. High fatality rates in hospitals with sophisticated infrastructures and health workers getting infected have exposed gaps in basic understanding of control of airborne diseases and their management in health care settings. The defence forces, specially the naval ships got affected all over the world. With history of pandemic diseases repeating at regular intervals, it is now amply evident that viral diseases will re-emerge in times to come, either in another novel form or as a bioweapon and effective and holistic mitigation measures will be crucial.2
Airborne or droplet borne. The infectious...
Airborne or droplet borne. The infectiousness of a disease is determined by the ability of the primary case to cause secondary cases in a susceptible population. It is based on Susceptibility – Infectivity-Recovery/Death (SIR) model and is quantified by the reproductive number (R0). The R0 is dependent on the proportion of susceptible population in a given cohort and its density and reduces with decongestion.3 The initial R0 for SARS CoV 2 at Diamond Princess, a cruise ship was 14.8 and was lowered to 1.78 with disembarkation of passengers and prevented almost 2000 extra individuals from getting infected.4 The transmission onboard ships would be both airborne through ventilatory ducts and by droplet transmission because of the close environment.
High vs Low Viral Load. Contact tracing data have found the contacts to be located mostly near the cases and did not spread to the rest of the population in the 2.2 square km slum area. Moreover, such transmission zones are comprised of only asymptomatic, mild or moderate cases, who have low viral load. High level of infectiousness in clusters of close quarters of susceptible hosts explains droplet and short distance aerosol transmission as has been endorsed by World Health Organisation (WHO) in their recent statement.5 Breaking the chain of transmission in a densely populated slum would have been possible because of droplet transmission from mildly symptomatic and asymptomatic cases and absence of airborne transmission from them. In the hospital setting however, high viral load in severely symptomatic patients and aerosol generating procedures may be accompanied by airborne transmission. This has been emphasised by several studies and endorsed by WHO.6
Way Ahead. Non-pharmacological Interventions of maintaining social distance, wearing of masks will have to be habit forming in the community. The hospitals have to bring in architectural modifications in their wards to include negative air pressure isolation facility alongwith HEPA filters and use of UV lights. Proper protective gears for health care workers need to be emphasised at all levels. Food habits for the general population will include known immune boosting products, also antioxidants and avoid junk; this will not only reduce the co morbidities like obesity and diabetes but will prevent mild infectious diseases. Future mitigating measures will have to emphasise on alteration of residences with proper ventilation, enough exhausts in bathrooms, multiple air exchange air conditioning system, which are essential measures for prevention and control of airborne diseases.
1. Khosla R, Allotey P, Gruskin S. Global health and human rights for a postpandemic world. BMJ Global Health 2020;5:e003548. doi:10.1136/ bmjgh-2020-003548
2. Prem K, Liu Y, Russell TW, et al. The effect of control strategies to reduce social mixing on outcomes of the COVID-19 epidemic in Wuhan, China: a modelling study [published correction appears in Lancet Public Health. 2020 May;5(5):e260]. Lancet Public Health. 2020;5(5):e261-e270.
3. JK Aronson, Jon Brassey, KR Nahtani. When will it be over? An introduction to viral reproduction numbers (R0 and Re). Available at https://www.cebm.net/covid-19/when-will-it-be-over-an-introduction-to-vi.... Accessed on 14 Aug 2020.
4. Zhang S, Diao M, Yu W, Pei L, Lin Z, Chen D. Estimation of the reproductive number of novel coronavirus (COVID-19) and the probable outbreak size on the Diamond Princess cruise ship: A data-driven analysis. Int J Infect Dis. 2020;93:201‐204.
5. Coronavirus: What is the Dharavi model being praised by WHO chief Tedros Adhanom. Available at https://www.indiatoday.in/india/story/what-is-the-dharavi-model-being-pr.... Accessed on 11 Aug 2020
6. World Health Organisation. Transmission of SARS-CoV-2: implications for infection prevention precautions. https://www.who.int/news-room/commentaries/detail/transmission-of-sars-c.... Accessed on 11 Aug 2020.