Coronavirus: is China’s rigorous home disinfection prudent disease control, falsely reassuring or overkill?
- Emphasising deep cleaning aligns with Beijing’s persistent view the virus can spread from surfaces, and may originally have been imported into Wuhan on goods
- Experts say better ventilation and air circulation, as well wearing masks, would better prevent the spread of Covid-19
The floor, walls, chairs and tables, toys, cooking pots and dishes, clothes and electronic appliances would be disinfected, a government statement said.
Bedsheets, clothes and pillowcases could be disinfected first and returned to the patient or treated as medical waste, the statement said. Unopened food in the refrigerator may be disinfected and retained, while products that have been opened must be treated as medical waste.
In other words, it is a textbook “terminal disinfection” procedure to thoroughly remove pathogens from an environment, just as a hospital ward does between patients.
The statement is based on China’s Law on Prevention and Treatment of Infectious Diseases, which stipulates there must be strict disinfection of sewage, waste, places and objects contaminated with the pathogens of infectious diseases, and local health authorities can carry out compulsory disinfection.
A disinfection protocol issued for Sars-CoV-2, the virus that causes Covid-19, by the National Health Commission last September, regulates how terminal disinfection for Covid-19 patients, such as their homes, should be carried out.
But scientists say such disinfection is unnecessary for Sars-CoV-2, and serves little purpose other than giving a false assurance of security. Instead, improved ventilation, as simple as opening windows, would greatly cut the risk of transmission in homes.
“The virus does not survive well on surfaces, so once the infected person is no longer present, it would be a short time before any virus on the surfaces would degrade and no longer be able to cause new infection,” said Colleen McLaughlin, an associate professor of epidemiology and chair of the population health sciences department at the Albany College of Pharmacy and Health Sciences in Albany, New York.
McLaughlin said if the infected individuals and their families were placed in isolation outside the home, all infectious viruses would be gone within a day, or even sooner. It was unnecessary to disinfect while no one was home.
“Opening windows or otherwise increasing air flow would speed up the process of degradation. The virus cannot become airborne from surfaces,” McLaughlin said.
Health agencies and studies show Sars-CoV-2 is transmitted mostly by droplets with a diameter of 5 microns or above that can travel up to 1.8 metres (6 feet) and usually fall to the ground, or by smaller aerosol particles that can get caught in air flows and move throughout a space, infecting people at further distances.
China, on the other hand, has been emphasising the dangers of fomite transmission, arguing it was the source of several outbreaks.
Fomite transmission involves people catching Covid-19 by touching their eyes, nose or mouth after touching the surfaces of objects that had been contaminated by Sars-CoV-2.
The fomite transmission theory was supported by a study in February by Kyoto Prefectural University of Medicine researchers who said the Omicron variant could survive as long as 193.5 hours on plastics and 21.1 hours on skin, which meant a higher chance of exposure for infection.
However, the study – published without peer review on preprint site bioRxiv – did not reveal how much of the virus was put in the lab study, a factor that greatly influences its chances of survival. Also, the study was completed under highly controlled laboratory conditions, an environment much easier for viruses to survive in.
Linsey Marr, a professor of civil and environmental engineering at Virginia Tech, said such lab studies could not be directly translated to how long viruses survived in the real world.
“There have been lab studies showing that the virus survives for many hours to days on different types of surfaces, but these studies start with unrealistically enormous amounts of virus in huge droplets – 100 times larger in volume than the largest droplets generated from the respiratory tract,” Marr said. “I do not think these studies alone should be used to gauge whether fomite transmission is likely to occur.”
A study by Marr’s team on virus contamination in university dormitories, published in the peer-reviewed journal Environmental Science & Technology Letters in December, found a high prevalence and concentrations of Sars-CoV-2 RNA on commonly touched surfaces, HVAC filters and exhaust grilles in rooms housing infected individuals, but detected no culturable virus on any surface.
On the other hand, the chance of fomite transmission was considered relatively low, according to peer-reviewed research.
In fact, a study by the University of Michigan found out exactly how much the risk from surface contamination of Covid-19 was lower than aerosol transmission: 1,000 times.
The two-year study published in Journal of Exposure Science and Environmental Epidemiology last month looked at public spaces on the university campus – including classrooms, rehearsal rooms, cafeterias, buses, gyms, student activity buildings and ventilation and air ducts – and concluded the estimated probability of infection was about 1 per 100 exposures to Sars-CoV-2-laden aerosols through inhalation and as low as one per 100,000 exposures from contacting contaminated surfaces in simulated scenarios.
The risk of infection from fomite transmission is well below the tolerable infection risk benchmark of 55 in 100,000 persons based on WHO’s Disability Adjusted Life Years (DALY) loss per person per year (PPPY) and disease/infection ratio observed during the Covid-19 pandemic. The study also found airborne transmission could be greatly reduced through mitigation methods such as increased ventilation, air filtration, capacity control and face coverings.
Chuanwu Xi, professor of environmental health sciences and global public health at University of Michigan’s school of public health, said improving ventilation was more meaningful than home disinfection.
“Improving ventilation in individual homes and big buildings is more efficient in reducing potential transmission of Sars-CoV-2. Simply opening windows when possible will contribute to the reduction,” said Xi, who led the study.
“Vaccination is the most powerful approach to protect the public from Covid-19, and wearing masks and regular personal hygiene such as hand washing are essential to reduce transmission.”
Routine and common sanitation were helpful in reducing transmission in the household and overdoing it was not necessary. “Home use of bleach is sufficient to disinfect rooms,” Xi said.
Liu Xiaofeng, deputy director of the Beijing Centre for Disease Prevention and Control, said “scientific and precise” disinfection work would be carried out before sealed-off residential areas reopened.
“The focus of disinfection in public areas would be knobs of building doors, handrails of stairs, keys of elevator buttons,” Liu said, adding that air in outdoor spaces would not be disinfected.
Tian Linwei, an environmental epidemiologist with the University of Hong Kong, said that while disinfecting and cleaning lift buttons or frequently touched public places could be useful, the plan could be flawed.
“In crowded places in Hong Kong, disinfecting public corridors or elevators might have some usage, but in other scenarios I doubt it and there could be drawbacks, including giving you a false perception that you are safe,” Tian said.
McLaughlin of Albany College said disinfection in public areas could benefit cutting transmission of other viruses, such as norovirus, which survived longer and had a higher risk of spreading from surfaces, but there was little advantage when it came to curbing Covid-19.
“In general, it is a good idea to clean and disinfect high-touch surfaces to protect from [viruses] that are spread in this way, but as far as we know, this type of transmission of the Covid virus is rare,” she said, adding that after mask-wearing, improving ventilation was one of the best ways to limit spread.
“Air circulation helps destroy the Sars-CoV-2 quicker in both the air and on surfaces. Air circulation also dilutes the virus in the air, which lowers risk by decreasing the number of virus particles inhaled,” she said.
If it was not possible to increase air circulation, then disinfection on a daily basis might help, but it depended on the timing, McLaughlin said. Disinfecting while people were using the building would be more helpful than at the start or the end of the day.