Virus survival as a seasonal factor in influenza and poliomylitis

Transmission of influenza A in human beings

Planning for the next influenza pandemic is occurring at many levels throughout the world, spurred on by the recent spread of H5N1 avian influenza in Asia, Europe, and Africa. Central to these planning efforts in the health-care sector are strategies to minimise the transmission of influenza to health-care workers and patients. The infection control precautions necessary to prevent airborne, droplet, and contact transmission are quite different and will need to be decided on and planned before a pandemic occurs. Despite vast clinical experience in human beings, there continues to be much debate about how influenza is transmitted. We have done a systematic review of the English language experimental and epidemiological literature on this subject to better inform infection control planning efforts. We have found that the existing data are limited with respect to the identification of specific modes of transmission in the natural setting. However, we are able to conclude that transmission occurs at close range rather than over long distances, suggesting that airborne transmission, as traditionally defined, is unlikely to be of significance in most clinical settings. Further research is required to better define conditions under which the influenza virus may transmit via the airborne route.

Review of aerosol transmission of influenza A virus

In theory, influenza viruses can be transmitted through aerosols, large droplets, or direct contact with secretions (or fomites). These 3 modes are not mutually exclusive. Published findings that support the occurrence of aerosol transmission were reviewed to assess the importance of this mode of transmission. Published evidence indicates that aerosol transmission of influenza can be an important mode of transmission, which has obvious implications for pandemic influenza planning and in particular for recommendations about the use of N95 respirators as part of personal protective equipment.

The effects of relative humidity and temperature on the survival of human rotavirus in faeces

The effects of relative humidity and temperature on the survival of human rotavirus in a thin layer of faeces on an impervious surface and on absorbent material was investigated using the indirect immunofluorescence technique in LLC-MK2 cells to titrate infectivity. Rotavirus was found to be very stable at low and high relative humidities but not in the medium range of relative humidity. Rotavirus infectivity was lost more rapidly under all humidities at 37 degrees C than at 4 degrees or 20 degrees C.

Airborne stability of tailless bacterial viruses S-13 and MS-2

The effect of relative humidity (RH) on the airborne stability of two small bacterial viruses, S-13 and MS-2, was studied. Poorest recovery of S-13 was obtained at 50% RH. Humidification prior to aerosol sampling significantly increased the recovery of S-13 at RH deleterious to the airborne virus. A commercial preparation of MS-2 suspended in a buffered saline solution showed a rapid loss of viability at RH above 30%, whereas a laboratory preparation containing 1.3% tryptone showed high recoveries at all RH studied. Dilution of the commercial MS-2 into tryptone broth conferred stability on the airborne virus. Humidification prior to sampling significantly reduced the viable recovery from aerosols of commercial MS-2, whereas the laboratory preparation was unaffected.

The inactivation of poliovirus in aerosols

Poliovirus type 1, strain LSc2ab, was directly sprayed in a static air cabinet at 20° C. and sampled afterwards with impingers. Virus inactivation during spraying was maximal in dry air; during storage maximal decay occurred at moderate humidity.

With regard to the mechanism of the inactivation the following facts have been observed: (1) The RNA in the virus decays simultaneously with the whole virus particle. (2) Oxidation does not play any significant role. (3) Incubation with L-cystine protects the virus against inactivation at 50° C. in aqueous suspension, but not against decay in aerosols.

On the strength of these observations it is concluded that in aerosols denatura-tion of the viral RNA is the cause of the inactivation of poliovirus. The decay in aerosols has some features in common with the thermal inactivation in aqueous suspensions at room temperature.

Survival of a picornavirus and its infectious ribonucleic acid after aerosolization

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