SPREAD OF THE COMMON COLD AND INFLUENZA

Professor R. Eccles,
Common Cold Centre,
Cardiff School of Biosciences,
Cardiff University, UK

Common cold: the most common disease
Common cold infections are so widespread that there can be very few humans who escape infection each year and most will suffer multiple infections. It has been estimated that adults suffer 2 to 5 colds per year, and infants and pre-school children have an average of 4 to 8 colds per year (Sperber 1994).

At least 120 million colds a year in the UK
If we accept an average incidence of two colds per person per year this means at least 120 million colds a year!

The economic impact of colds and flu
There are no reliable figures for the impact of common cold and flu on the economy. If one takes into consideration lost days from work and school together with the with hospital admissions and mortality in babies and the elderly, plus exacerbation of asthma and otitis media with effusion the impact must run into many hundred million pounds each year. Even a moderate reduction in the incidence of colds and flu would therefore be of significant economic benefit.

How colds are spread is still uncertain
Despite a considerable amount of research we still do not know exactly how colds are spread. We know that when someone is infected they can shed millions of virus particles in the mucus they produce, and that the home is an important site for the spread of infection, but we are still uncertain how these viruses make the journey from one nose to another!

Aerosol versus dirty fingers
It is generally accepted that common colds can spread by aerosol particles of infected mucus generated by coughs and sneezes but there is evidence that transfer also occurs via fingers contaminated from contact with the infected nose. Infection is passed on to another person either by handshaking or via surfaces such as handkerchiefs and tissues, wash tap and door handles, telephones or other surfaces touched by an infected person – even via the surface of shared playing cards. The problem is that we actually do not know which of these routes of transmission is the most important.

Unusual experiment to demonstrate aerosol transmission of colds
Some experiments (D’Alessio et al. 1984, Dick 1987) have gone to great lengths to demonstrate that colds can be spread via aerosol transmission. In one experiment a group of volunteers with colds played cards with a healthy group of volunteers for a period of twelve hours whilst they were prevented from touching their nose or eyes by means of a large neck collar and arm brace. Just over half the healthy volunteers developed colds and the experimenters concluded that infection could only have occurred via aerosol transmission.

Are coughs and sneezes not so infectious?
Although there is evidence that common colds are spread by aerosol transmission there is still controversy as to whether this is the major route of transmission since there is little evidence that coughs and sneezes actually produce an aerosol of infected nasal mucus. In one study volunteers with colds were housed in a room and the air sampled for the presence of virus, yet despite the fact that 82% of the air in the room was sampled the tests failed to detect any virus (Gwaltney, 1980). When volunteers were asked to cough or sneeze directly onto a surface designed for detection of viruses, virus was recovered from only 2 in 25 volunteers (Hendley, 1973).

Kissing is OK
You are unlikely to catch a cold by kissing as saliva contains very little virus and the mouth is not an area that is infected by cold viruses. When volunteers infected with common cold virus have kissed cold free volunteers it has proved remarkably difficult to spread infection and in one experiment from 16 instances of kissing for up to one and a half minutes only one case of cross infection occurred (D’Alessio et al. 1984).

Viruses can enter the nose via the eye
Since tear fluid from the eyes drains down a tiny duct into the nose, virus that contaminates the eye readily enters the nose in tear fluid and the eye acts as an entrance for infection to the nose. This route of infection may be important when the eyes are rubbed with contaminated fingers.

Training children in personal hygiene can give results
In one study (Corley et al. 1987) 16 asthmatic children aged between 4 and 8 years were trained to alter their behaviour and not to touch their nose and eyes so frequently. The aim was to see if this behavioural change could help reduce the number of infections and the incidence of asthma attacks associated with common cold. A reduction in self-inoculatory behaviour was associated with a 45% reduction in common cold-associated asthma attacks and a 47% reduction in laboratory diagnosed common cold infections. Although the change in self-inoculatory behaviour in children did not abolish common cold infection the reduction in the incidence of colds could have a very large impact on spread of colds in schools.

Viruses do remain viable on contaminated surfaces
Indications are that cold viruses deposited on surfaces, either from the hands or the settling of aerosol particles, can remain viable on that surface – and in large numbers – for several hours (Gwaltney and Hendley 1982, Sattar et al. 1993). By contrast with bacteria the "infectious dose" i.e the number of viral particles required to cause infection may be very small (Smith et al. 1966, Couch 1990). For rhinovirus the infective dose may be less than 1 TCID (Couch 1990). Reed (1975) and Ansari et al. (1991) have shown that infectious viruses can be recovered from naturally contaminated objects in the surroundings of persons with rhinovirus colds and that clean hands can readily pick up the virus by touching or handling such objects.

Hand disinfectant can reduce infection
The importance of contaminated fingers in spreading the common cold was demonstrated in a study in which volunteers applied aqueous iodine (2%) to the fingers. None of eight volunteers became infected when exposed to rhinovirus immediately after treatment whereas all of seven placebo-treated volunteers became infected (Gwaltney et al. 1980).

But what about influenza?
Influenza can be spread from person to person by aerosol transmission due to sneezing and coughing. Like colds it is probably also spread by hand and surface transfer although there is less supporting evidence than for colds as most experimental work as been with the Rhinovirus. In many animal species such as ducks, influenza is spread by the faecal route rather than by aerosol (Shortridge 1997). Both Influenza A and B have been shown to survive on hard surfaces such as stainless steel and plastic for 24-48 hours (Bean et al. 1982). They survived for up to 12 hours on absorptive surfaces such as cloth, paper and tissues. Influenza A virus was transferred from contaminated stainless steel surfaces to hands for 24 hours after the surface was inoculated. Transmission of influenza virus resulting in an outbreak in a nursing home may have been mediated by staff either via contaminated hands or fomites (Morens and Rash 1995).

Other Respiratory Viruses
Under ambient conditions Human Parainfluenza Virus (HPIV) (Ansari et al. 1991) and Respiratory Syncytial Virus (RSV) (Hall et al. 1980) may survive sufficiently long enough in the environment to allow transfer of infectious virus to hands in contact with contaminated surfaces. The transfer of HPIV from stainless steel discs to clean fingers supports a role for fomites in the contamination of hands with viruses (Ansari et al. 1991). Parainfluenza virus could be recovered from non-absorptive surfaces for as long as 10 hours when the surface remained moist. Virus persisted on the hands for a minimum of 1 hour and on dry surfaces for up to 2 hours. Parainfluenza virus may have an infective dose via the nasal route of less than 80 TCID (Smith et al. 1966).

And finally, a useful quote
"The common cold and other respiratory viruses are the most frequent acute illnesses in the world. Although these illnesses are mild in the majority of patients, they are leading causes of morbidity and even mortality in certain groups or populations. Their transmission is exceedingly easy, and treatment is difficult. … For all these viruses, attention to hand washing (especially amongst health-care personnel) needs to be elevated to the level of standard care". (Smith 1995)

References
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Bean B, Moore BM, Peterson LR, Gerding DN and Balfour HH. Survival of influenza viruses on environmental surfaces. J Infect Dis 146 (1982) 47-51.

Carter CH, Hendley JO, Mika LA, Gwaltney JM. Rhinovirus inactivation by aqueous iodine in vitro and on skin. Proceedings of the Society for Experimental Biology and Medicine 165 (1980) 380-383.

Couch RB (1990) Rhinoviruses. In Fields Virology, eds Fields BN, Knipe DM, Chanock RM, Hirsch MS, Melnick JL, Monath TP and Roizman B. p607-629. Raven Press, New York.

D'Alessio DJ, Meschievitz CK, Peterson JA, Dick CR, Dick EC. Short-duration exposure and the transmission of rhinoviral colds. J Infect Dis 150 (1984) 189-194.

Dick EC, Jennings LC, Mink KA, Wartgow CD, Inhorn SL. Aerosol transmission of rhinovirus colds. J Infect Dis 156 (1987) 442-448.

Corley DL, Gevirtz R, Nideffer R, Cummins L. Prevention of postinfectious asthma in children by reducing self-inoculatory behaviour. Journal of Pediatric Psychology 12 (1987) 519-531.

Gwaltney JM. Epidemiology of the common cold. Annals New York Academy of Sciences (1980) 54-59.

Gwaltney JM, Moskalski PB, Hendley JO. Interruption of experimental rhinovirus transmission. J Infect Dis 142 (1980) 811-815.

Gwaltney JM and Hendley JO. Transmission of experimental rhinovirus infection by contaminated surfaces. Am J Epidemiol 116 (1982) 828-833.

Hall CB, Douglas R and Geiman JM. Possible transmission by fomites of respiratory syncytial virus. J Infect Dis 141 (1980) 98-102.

Hendley JO, Wenzel RP and Gwaltney JM. Transmission of rhinovirus colds by self-inoculation. New Engl J Med 288 (1973) 1361-1364.

Morens DM and Rash VM. Lessons from a nursing home outbreak of influenza A. Infect Cont Hosp Epidemiol 16 (1995) 275-80.

Reed SE. An investigation on the possible transmission of rhinovirus colds through indirect contact. J Hyg 75(1975) 249-258.

Sattar SA, Jacobsen H, Springthorpe S, Cusack T and Rubino J. Chemical disinfection to interrupt the transfer of Rhinovirus type 14 from environmental surfaces to hands. Appl EnvironMicrobiol 59 (1993) 1579-1585.

Shortridge KF. The influenza conundrum. Journal of Medical Microbiology 46 (1997) 813-815.

Smith MBH. Transmission and therapy of common respiratory viruses. Current Opinion in Infectious Diseases 8 (1995) 209-212.

Smith CB, Purcell RH, Bellanti JA and Chanock RM. Protective effect of antibody to parainfluenza type 1 virus. New Engl J Med 275 (1966) 1145-1149.

Sperber SJ. The common cold. Infections in Medicine 11 (1994) 235-242.