A micron is a millionth of a meter. A strand of human hair is approximately 50 microns wide while the red blood cell carrying oxygen in our blood is just 5 microns wide. One sneeze or cough may carry about 3,000 droplets, with each droplet being more than 5 microns across. When the suspended particle is smaller than 5 microns, it is called an aerosol.
An interesting scientific letter published last week in the New England Journal of Medicine examined the stability of the COVID-19 virus compared to that of the severe acute respiratory syndrome (SARS) virus in experimental conditions.
The researchers report that the COVID-19 virus exists in aerosols for three hours before decaying. The half-life is around 1 hour, which means that the quantum of viruses diminishes to half its original value in one hour, the implication being that infectivity mitigates with time.
The same virus was found to last for three days on plastic and steel but only for four hours on copper. Cardboard, however, permitted the virus to be present for almost a day. The researchers suggest that their results indicate that aerosol and fomites-based1 transmission of COVID-19 is plausible as the new coronavirus can remain viable and infectious in aerosols for almost three hours and on surfaces for three days.
The experiment explains how a patient infected with COVID-19 viral loads in the upper respiratory tract can transmit the virus to others in the form of aerosols (<5 microns) or droplets (>5 microns).
The researchers generated aerosols using nebulisers and collected samples of the virus on a gelatine filter. Next, they tested the infectivity of the virus on Vero cells2. The hallmark of this study is that it used infectious viruses that were able to spread infection. Older studies used the polymerase chain reaction, a chemical test that examines only the virus’s genome while the virus may be dead for all practical purposes.
The fact that cardboard can hold the COVID-19 virus for almost a day means that your parcel – if sent more than a day earlier – is largely harmless, bearing in mind that the handler is not suffering from COVID-19. It would be prudent to disinfect as many articles in cardboard or plastic packaging with 70% ethanol or 0.5% sodium hypochlorite.
The Centre for Disease Control and Prevention emphasises that the majority of cases of transmission of the new coronavirus is not due to the touching of infected surfaces.
Of course, common sense dictates that frequent washing of ones’ hands and disinfecting commonly touched surfaces are important for virus prevention. No wonder that most doctors in my hospital use their shoes to push open doors, avoiding door handles as much as possible. Also, because soap breaks the virus into pieces, one must wash one’s hands as frequently as possible, for one never knows what one may have touched in the course of the day.
Let’s face it, most objects touched in a hospital or office are not disinfected. Hand washing is one of the most effective ways to prevent the COVID-19 virus attacking you. Incidentally, hand washing as a means of prevention was first advised by a Hungarian doctor named Ignaz Semmelweis, in the 19th century. Born in 1818, he went on to work at the Allgemeine Krankenhaus teaching hospital in Vienna. Semmelweis initiated a mandatory protocol of hand washing for physicians and became known as the “father of infection control”.
Now, it would be prudent to keep in mind that the letter published in the New England Journal of Medicine only documents experimental data by simulation. That said, the message is stark for doctors and health workers in hospitals. A patient with coronavirus in the ICU is ‘red-hot’ because he can contaminate not only the objects around him but also the air around him. The virus-infected aerosol hanging around the patient could prove to be lethal for nurses and doctors treating the patient. Intubation for mechanical ventilation and ventilation itself will aggravate the release of the coronavirus from out of the person’s body and into the air.
Hospitals are confined spaces and every epidemic has killed many health workers. Intensive care doctors in Italy for example have rented flats or even occupy nearby hotels in order to avoid carrying the infection back to their families. Hugging and kissing children is out of the question. Doctors who continue to stay in their homes isolate themselves after a hot shower. They have to sleep alone, some on the sofa. One must salute Dr Li Wenliang, the Chinese doctor who tried to warn people about the coronavirus outbreak and died treating patients in Wuhan. There have been many more deaths of medical personnel treating patients.
The situation regarding aerosol infection however may be a bit different in open spaces. There is no science to prove that a breeze may dilute the density of viral load in the air but this is probable. An elevator in a hospital should be a hotspot for potential virus spread but not so a park. The experiment cited compared the stability of the SARS virus with SARS-CoV-2. There was little difference in aerosols between the two viruses.
SARS was first reported from Guangdong in November of 2002. The cause was ascertained to be an animal virus that had hopped from bats to humans via a palm civet or a raccoon. In less than a year, SARS infected 8,098 people in 26 countries, of whom 774 died. The case fatality rate was about 10% overall but was 40% among patients older than 60 years. It is worth mentioning that approximately 20% of reported cases of SARS were health care workers. Mercifully, SARS disappeared in a couple of years. There have been no reports of SARS since 2004 despite ongoing surveillance.
The largest data on COVID-19 so far has been reported by the Chinese Centre for Disease Control and Prevention, and which includes more than 72,000 cases. Of these, 44,672 cases were confirmed based on positive viral nucleic acid testing. Mild disease was present in 81% of cases, severe cases were 14% while 5% of patients were considered critical. Case fatality overall was 2.3% but 15% in those above 80 years and 8% in people in their 70s. Crucially, only 3.8% cases involved health care personnel (1,716 of 44,672 confirmed cases). Some 15% of cases among health workers were classified as severe or critical. It is abundantly clear that health care workers are a vulnerable cohort that needs to be constantly alert as well as supported.
The Lancet in a recent editorial emphasised protection for health care workers during the current pandemic. The local Chinese media has reported that by the end of February, at least 22 health workers had died, whereas in Italy 20% of health care workers have become infected and some have died. Health care workers in intensive care units in particular need proper protective equipment. The numbers from Italy are appalling: thus far, at least 23 doctors have perished while 4,824 health workers have been infected by the coronavirus, according to the Italian Federation of Doctors. Italy has reported the highest number of deaths, at 6,077, thus far.
Through all these efforts, remember that prevention is much, much better than cure. Firstly, there is no evidence that the experimental study translates in its entirety to real life. It would be common sense to wash ones’ hands as much as possible with soap and water before touch your face. If a person sneezes on a surface and you touch it, you could get infected. You will most probably, too. You will also touch door knobs, railings, walls and your desk, etc. So wash your hands.
However, it is not yet clear how many viruses are needed to infect someone. That the virus may last for three hours in aerosol in simulated conditions has been shown but there is no evidence that such is the case in open spaces as well. A lingering viral presence in air may not be infective. A simple disinfectant is enough to decontaminate any surface. The brand of soap or disinfectant does not matter.
Food is not considered a mechanism for transmission, but heating or reheating food will kill the virus. In case you are compelled to venture out, have a good shower or bath when you get back. Maintaining some distance from other people, ill or not, is good sense. Wearing a mask may provide protection but will almost certainly prevent an asymptomatic carrier from spreading the virus. But as explained earlier, the scenario for health workers at work in hospitals is far more grim. Which is why the fact that Indian medics treating COVID-19 patients around the country lack adequate protective gear is so disturbing.
Deepak Natarajan is a cardiologist based in New Delhi.