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OP-ED: What we need to know about the transmission of Covid-19

  • Published at 10:00 pm July 15th, 2020
covid test
Photo: MAHMUD HOSSAIN OPU

Waiting rooms, mosques, and open-plan offices can become hotspots

Covid-19 is transmitted primarily through respiratory droplets and direct contact with infected persons, or indirect contact with surfaces laden with virus particles from infected persons. Under certain circumstances, Covid-19 can potentially spread through airborne transmission. 

Droplet and contact transmission of Covid-19 occurs when an uninfected person is exposed to an infected person’s respiratory droplet through direct, indirect, and close contact. When a person with Covid-19 coughs, sneezes, talks, or shouts, respiratory droplets that include SARS-CoV-2 can reach the mouth, nose, or eyes of an exposed individual and cause infection. 

Infectious respiratory droplets can also fall on nearby surfaces where the virus can remain viable for several hours to days. A susceptible person touching these contaminated surfaces and subsequently touching his or her face without washing hands can get infected. More recently, there have been concerns about airborne transmission of SARS-CoV-2. 

Airborne transmission occurs when microdroplets (droplet nuclei usually <5 micrometres in diameters) containing infectious pathogens are expelled through coughing, sneezing, talking, or singing. These microdroplets can suspend in the air for a long distance and time. 

If a healthy person shares the same airspace and inhales that contaminated air, he or she might get infected. Airborne transmission has been observed with other respiratory viruses, such as influenza, and there is now limited data available to suggest SARS-CoV-2 may also be transmitted by airborne routes. However, the risk of airborne transmission is mostly within confined spaces. 

Transmission hotspots

It is increasingly important to understand how, when, and where the transmission is most likely to occur, to suggest prevention strategies. A person infected with SARS-CoV-2, with or without symptoms, may transmit Covid-19 to others. A SARS-CoV-2 infected person can start transmitting the virus from one to three days prior to symptoms onset and up to a couple of weeks after the onset of symptoms. Bangladesh has one of the highest population densities in the world, which poses a unique challenge in the prevention of Covid-19 transmission within communities and hospitals. 

In Bangladesh, high-risk places may include urban households (building structure), dormitories, open-plan offices, mosques, hospitals, clinics, doctor chamber waiting-areas, and public transportation.

The WHO-China joint report showed that around 78-85% of clusters occurred within household settings in China, which suggests the home can be a source of infection if appropriate infection prevention measures are not followed. The most likely pathway of household transmission could be poor ventilation (less air exchange), close and prolonged contact, sharing food, sharing beds or rooms without any precaution, and a lack of handwashing.

Open plan office spaces can be hotspots for airborne transmission of Covid-19, which has been observed in a call centre in South Korea, where 94 out of 131 people working in an open-plan office were infected. 

Crowded living conditions in dormitories or barracks can also be hotspots for airborne transmission as observed in Singapore and possibly in Bangladesh. Hospital-acquired Covid-19 transmission among health care providers, patients, and family caregivers have been widely reported. 

In Bangladesh, most hospitals, clinics, and even the doctor consultation rooms lack basic building designs that can provide sufficient air exchange, which can promote airborne transmission. Moreover, these facilities often have limited access to handwashing stations with running water and soaps further aiding contact transmission of infectious disease. 

Irregular and non-standard personal protective equipment (PPE) supply and use also contribute to health care-associated infection. In open spaces like playgrounds and streets, the risk of Covid-19 transmission, however, remains low. A high number of people congregated on the footpath are less likely to transmit the disease when compared with the same number of people in closed environments. However, if a person infected with SARS-CoV-2 coughs or sneezes directly on someone’s face, the risk of infection is high, even in open spaces. 

Infection prevention and control measures

Rapid identification of Covid-19 cases, isolation of cases, and quarantining people who were in contact with the infected person are crucial in reducing transmission of the disease. However, in resource-poor settings like Bangladesh, with high background rates of community transmission, optimal testing, and contract tracing for Covid-19 might not be feasible. While we wait for a vaccine, the effective and appropriate universal use of face masks should be promoted.  

There have been many controversies regarding the use of face masks from the beginning of this pandemic. As new evidence emerges, it is becoming clearer that the use of face masks will have to be the “new normal.” Due to the shortage of PPE and the increased risk of aerosolization of airborne particles within health care settings, the use of N95 respirators should be restricted to front line health care workers. 

It is advisable for community members to adhere to the use of three-layered fabric masks. A fabric mask will not protect against microdroplets, but can filter up to 90% of larger respiratory droplets. However, use of face masks alone is not sufficient to prevent transmission of Covid-19. Consistent and appropriate use of face masks in conjunction with practicing other proven control measures such as frequent handwashing, covering sneezes and coughs, maintaining physical distancing, and avoiding crowded spaces where possible will help keep the numbers of Covid-19 low, potentially avoiding intermittent lockdowns and helping the economy breathe as well. 

Lastly, moving forward, public health professionals should work closely with experts from built-environment disciplines, to better design buildings, homes, hospitals, and work-spaces which will ensure appropriate ventilation and limit the transmission of not only SARS-CoV-2, but potentially other respiratory viruses.

Md Saiful Islam, PhD, is Researcher (Infection Prevention and Control), University of New South Wales, Sydney, Australia. Dr Nusrat Homaira, PhD, is Senior Lecturer (Respiratory Epidemiology), University of New South Wales, Sydney, Australia.

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