It turns out that there is a very good reason why we are taught from such a young age to cover our mouths when sneezing or coughing.
Up to 20,000 viruses are released in the average cough, which is enough to infect many people, especially those who are not vaccinated.
Julian Tang, a consultant at Singapore’s National University Hospital’s Division of Microbiology, says that the normal cough produces as many as 3,000 tiny droplets.
Going by existing research on influenza viral levels in nasal secretions, and assuming that each droplet from a cough measures between 1 and 5 micrometers (one thousandth of a millimeter) in diameter, the viruses in a single cough quickly become hard to count.
Tang says, “Based on this research and assuming about 3,000 droplets are produced per cough, this range of influenza viruses produced per cough is about 195 to 19,500.”
“This (3,000) is also the number of droplets estimated to remain suspended in air for long periods — so-called droplet nuclei. Larger droplets carrying influenza viruses may also be produced during a cough, but these will fall to the ground relatively quickly and will no longer be considered to be significant in the airborne transmission of influenza,” he said.
The new H1N1 influenza virus spreading around the world has inspired governments around the world to re-educate and encourage people to observe good personal hygiene practice.
A TV advertisement in Indonesia shows a young woman scolding an admiring man at a village sing-a-long, telling him to go to a health clinic because “that’s not a normal cough.”
Directed toward the uneducated populations, the advertisements are set to a dangdut (traditional pop music) theme and have an easy-to-remember slogan and theme song.
Experts are unsure how to qualify an infective dose when it comes to a flu virus.
As a guideline, previous research has found that it only takes 1 to 10 organisms to cause viral hemorrhagic fevers, and 10 to 100 organisms to cause viral encephalitis.
Tang says an infective dose of flu virus depends on various factors such as the constitution and health of people breathing in these droplets and whether they had been previously vaccinated.
“It is difficult to give an exact number for the infectious dose — and this may even differ for the same individual throughout the year. But probably for immune people, the infectious dose will be higher than for non-immune people — hence, the benefits of vaccination,” Tang says.
“Those previously vaccinated or naturally infected to the same or similar virus can develop a rapid antibody response and clear the virus in the respiratory tract before the virus can take hold and cause disease”¦(but) even immune hosts may develop symptoms if the viral load exposure is sufficiently high,” he added.
Doctors say most airborne flu transmissions occur within a one-yard proximity, or by direct physical contact with contaminated objects.
“Wearing masks may well help to reduce the transmission of these infections, as well as covering the mouth with your hand or a tissue when coughing or sneezing — simply by using a barrier to prevent dissemination of the virus,” Tang says.
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