Existing measures still needed to curb transmissions through droplets

Prof Dr Anselm Su Ting of Universiti Malaysia Sarawak’s (Unimas) Faculty of Medicine and Health Sciences (top left panel) speaks during the virtual talk session as (from top right panel, clockwise) Dr Ooi Mong How, senior consultant paediatrician at Sarawak General Hospital; Kuching South City Council (MBKS) mayor Datuk Wee Hong Seng; and Billy Sujang, state chief environmental health officer from the Ministry of Local Government and Housing, look on.

KUCHING: Even with ventilation improvements to curb Covid-19 transmissions through aerosols, other measures, including physical distancing, surface decontamination, and the use of personal protective equipment (PPE), will still need to be practised in order to curb transmissions through droplets.

Comparing droplet and aerosol modes of Covid-19 transmission, Prof Dr Anselm Su Ting of Universiti Malaysia Sarawak’s (Unimas) Faculty of Medicine and Health Sciences said that ventilation control was not very useful against droplet transmissions of Covid-19.

“This is because typically the larger size of droplets will be pulled down by gravity and drop onto surfaces. No matter how you improve ventilation, droplet transmissions can still occur.” 

He explained that the existing measures of physical distancing, personal hygiene, surface decontamination, and the use of PPE were useful against both droplet and aerosol transmissions of the virus.

“However, for aerosol transmissions, we need an additional control measure which is ventilation control in order to reduce the risk of transmission through this mode.”

He said this during a virtual talk session on the standard operating procedure (SOP) on ventilation improvement at non-residential buildings during the Covid-19 pandemic held via Zoom on Tuesday (Sept 14).

“Droplets usually spread directly from face to face and the spread is usually limited by gravity. These can contaminate surfaces and spread but usually within a confined space.”

As for aerosols, Dr Su said these could be suspended in the air and be spread by air currents and even beyond a room.

As such, he said studies had shown that the transmission range of large droplets was often within one to three metres whereas aerosol clouds could travel across further distances of around five to six metres.

“Droplets would be usually get trapped in the upper respiratory tract while aerosols can penetrate into the lower respiratory tract.”

In terms of particle sizes, he said particles of around 100 microns or less would usually be trapped on the upper respiratory tract while smaller-sized particles of 10 microns and under could penetrate deep into the respiratory system.

“Particles which are less than 2.5 microns can go into the alveoli and this is where infections can occur, such as pneumonia and so on.”

Dr Su emphasised that the spread of Covid-19 through aerosols had become an important aspect to be looked into in an effort to control transmissions, especially in view of the highly infectious Delta variant.