Routes of Transmission of the Influenza Virus

Routes of Transmission of the Influenza Virus

Scientific Evidence Base Review

1

Routes of Transmission

DH INFORMATION READER BOX

Policy HR / Workforce Management Planning / PCelinrfiocraml ance

Estates Commissioning IM & T Finance Social Care / Partnership Working

Document Purpose For Information

Gateway Reference 15652

Title

Author Publication Date Target Audience

Routes of Transmission of the Influenza Virus: Scientific Evidence Base Review

Pandemic Influenza Preparedness Team 22 Mar 2011 Supporting Documents for UK Influenza Pandemic Preparedness Strategy

Policy

Circulation List

Supporting Documents for UK Influenza Pandemic Preparedness Strategy

Description

Document summarising the science evidence base underpinning influenza modes of transmission as outlined in the 2011 UK Influenza Pandemic Preparedness Strategy

Cross Ref

N/A

Superseded Docs N/A

Action Required

N/A

Timing Contact Details

N/A

Dr John Connolly Pandemic Influenza Preparedness Team Department of Health Skipton House, 80 London Road London, SE1 6LH (020) 7972 5303

0

For Recipient's Use

2

Routes of Transmission

Routes of Transmission of the Influenza Virus

Scientific Evidence Base Review

Prepared by: Dr Ben Killingley, University of Nottingham; Allan Bennett, Microbiology Services Division, HPA; Professor Jonathan Nguyen Van-Tam, University of Nottingham and HPA. This review was commissioned by the Department of Health in October 2010. The document was subsequently reviewed and endorsed by the Scientific Pandemic Influenza Advisory Committee (SPI). In general, the review examined scientific literature published up until the end of 2010. This document thus represents a contemporary summary of the evidence base for the routes of transmission of influenza virus to humans, as of 2010. It is anticipated that additional informative studies in this area will be published over the course of 2011 and 2012. The review will therefore be updated periodically to reflect any additions to the scientific literature that might alter any of its conclusions. All of the figures in this review have been reproduced with the permission of the copyright holders.

3

Routes of Transmission

Contents

Contents..................................................................................................................................... 4 Executive summary.................................................................................................................... 5 Glossary ..................................................................................................................................... 8 Abbreviations ............................................................................................................................. 9 Introduction .............................................................................................................................. 10 Definitions ................................................................................................................................ 12 Search Methods ....................................................................................................................... 14 1. Studies assessing influenza virus deposition and survival in the environment.................. 15

Search Methods ................................................................................................................... 15 Contact transmission ............................................................................................................ 16 Virus survival ? Hands .......................................................................................................... 16 Virus Survival ? surfaces ...................................................................................................... 17 Detecting virus in natural conditions ..................................................................................... 18 Discussion ............................................................................................................................ 19 Droplet Transmission............................................................................................................ 21 Aerosol Transmission ........................................................................................................... 21 Aerosol Physics .................................................................................................................... 22 Aerosol Survival.................................................................................................................... 24 Detecting aerosols produced by infected patients ................................................................ 25 Discussion ............................................................................................................................ 27 2. Outbreak Investigations .................................................................................................... 29 Search Methods ................................................................................................................... 29 Reports ................................................................................................................................. 30 Discussion ............................................................................................................................ 41 3. Prospective intervention studies in the setting of natural infection .................................... 43 Search Methods ................................................................................................................... 43 Studies.................................................................................................................................. 43 Discussion ............................................................................................................................ 50 4. Human Challenge Studies ................................................................................................ 52 Search methods ................................................................................................................... 52 Studies.................................................................................................................................. 52 Discussion ............................................................................................................................ 54 5. Animal Studies .................................................................................................................. 56 Search Methods ................................................................................................................... 56 Experimental models ............................................................................................................ 56 Transmission Factors ........................................................................................................... 57 Discussion ............................................................................................................................ 60 6. Modelling Influenza Transmission ..................................................................................... 61 Search Methods ................................................................................................................... 61 Studies.................................................................................................................................. 61 Discussion ............................................................................................................................ 66 Conclusion ............................................................................................................................... 68 References............................................................................................................................... 73

4

Executive summary

1. There is sound evidence supporting influenza virus survival on fomites and hands for periods consistent with the possibility of onward transmission.

2. The data are relatively heterogeneous regarding the likely survival time of virus deposited on surfaces and factors such as virus concentration of the inoculum, type of surface and temperature and humidity clearly affect virus survival. Thus, it is not possible to provide absolute numbers or ranges for survival times further than to say that estimates lie in the range of a few hours to several days.

3. In general the data support longer survival on hard (non-porous) surfaces than on softer (porous) items.

4. Few data demonstrate the recovery of viable virus from surfaces contaminated by patients with natural or experimental influenza compared with recovery of viable virus from surfaces after deliberate inoculation. This might reflect limitations in sampling efficiency, study designs, or virological techniques and does not reliably indicate that contact transmission is relatively less important than droplets/aersosols.

5. The indirect contact route of transmission is the most vulnerable to natural interruption because it involves multiple stages. In order for infection to be transmitted; a) titres of virus in excess of the human infectious dose must be shed, b) deposited virus must survive, c) high titres must be collected via hands, d) virus must survive on hands, e) hands must deposit an infectious dose of virus on target cells.

6. Whilst there are unanswered questions about the relative importance of contact transmission compared with other routes, contact transmission cannot be excluded.

7. Coughing and sneezing produce a `respiratory spray' consisting of large particles (droplets) and small particles (aerosols).

8. From the available evidence there is no doubt that droplet transmission of influenza occurs. 9. Aerobiological studies reveal that the vast majority of pathogens excreted during human

coughing and sneezing are contained within droplets. 10. These particles behave ballistically and fall out of circulation within a few feet (range is

proportional to size).

5

 ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download