Influenza A (H1N1) Blog

In the next text we shall see how Influenza can be transmitted by air. Now we shall see the role of contact in its transmission.

Source: Wikimedia

Transmission of Influenza by contact can be direct or indirect. Direct contact occurs when we come in contact with the secretions of a sick person and we place our hands on our eyes, mouth or nose. Indirect contact occurs when we touch objects or surfaces contaminated by someone expelling the virus and we put our hands on one of the aforementioned mucous tissues.

Avoiding direct contact is something that is relatively simple, if we know that someone has the flu, we can keep certain precautions. However, in indirect contact, it is much more complicated, especially for children who are very active and constantly touch their mouth or eyes with their hands and stay in schools and daycare centers with a high number of colleagues. Frequenting public places is also a guarantee of contact with surfaces and objects touched by other people who are not aware of whether they are ill or not.

The most important thing in the case of indirect contact is the viability of the virus exposed in the environment. What is the amount of influenza present in the place and for how long does it remain infective. On porous surfaces, such as paper towels and cotton clothes for instance, the virus is no longer detected after about 12 hours, and when in contact with the hands it lasts for about 5 minutes. However, on smooth surfaces like steel, the virus remains viable for more than a day, up to 48 hours, and for more than 15 minutes on the hands after contact. [1]

And for how long does the influenza virus last on cash notes? It lasts for a longer period of time on Swiss notes, which is made of wax-coated cotton fiber that gives them a smooth surface. Virus in concentrations close to that detected on patients in acute phase can last for more than 3 days. If they are protected by mucus, which helps regulating the humidity and salinity in which the Influenza is stable, it recovers and infects cells in culture for up to 17 days! [2]

The nasopharyngeal swab from children deposited directly on the note allowed the virus to recover on half of the notes after one day, and on a third of them after 48 hours.

Children are more prone to transmission by contact not only because they are more active but also because they develop a much higher viral load during the infection, due to the lower immunity to the influenza, as a result of an immune system that came into contact with the virus a few times.

An experiment conducted on daycare centers and houses with children detected the genetic material of the virus on objects during various seasons (Here, it is worth emphasizing that detecting the genetic material does not mean detecting the infective virus, but it is a good start) and discovered that, although in the summer there is no Influenza RNA on objects, in winter the number of infected objects rises to 23%, and in spring more than half the tested objects had a positive result. [3]

Once the hands are contaminated, studies with virus knowingly transmitted by contact, such as the rhinovirus, shows us that we put our hands on our eyes, mouth and nose on an average of 2.5 times per hour. This is when we are not being observed (or we do not know). When we are facing another person, this rate increases to about 10 times. [4]

Therefore, always wash your hands during a flu outbreak. Long washes, with soap or alcohol solutions in concentrations of at least 60%, are safe ways of preventing the flu. Once again, if you have the flu, avoid leaving the house, and if you do, always cover your mouth or nose when coughing or sneezing with a handkerchief and immediately dispose of it.

Sources:

[1] Bean B, Moore BM, Sterner B, Peterson LR, Gerding DN, & Balfour HH Jr (1982). Survival of influenza viruses on environmental surfaces. The Journal of infectious diseases, 146 (1), 47-51 PMID: 6282993

[2] Thomas, Y., Vogel, G., Wunderli, W., Suter, P., Witschi, M., Koch, D., Tapparel, C., & Kaiser, L. (2008). Survival of Influenza Virus on Banknotes Applied and Environmental Microbiology, 74 (10), 3002-3007 DOI: 10.1128/AEM.00076-08

[3] BOONE, S., & GERBA, C. (2005). The occurrence of influenza A virus on household and day care center fomites Journal of Infection, 51 (2), 103-109 DOI: 10.1016/j.jinf.2004.09.011

[4] WEBER, T., & STILIANAKIS, N. (2008). Inactivation of influenza A viruses in the environment and modes of transmission: A critical review Journal of Infection, 57 (5), 361-373 DOI: 10.1016/j.jinf.2008.08.013