What did we learn from the Influenza pandemic?

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A lecture given at the BOHS Conference in Harrogate in 2010.

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  • The new virus caused high levels of summer infections in the northern hemisphere, and then even higher levels of activity during cooler months in this part of the world. Pregnant women, younger children and people of any age with certain chronic lung or other medical conditions appear to be at higher risk of more complicated or severe illness. A significant percentage of people age 65 and older do have some immunity against the pandemic virus.
  • Difficult to be sure about the mortality rate within sub-populations at the moment
  • The 1918 pandemic, which was by far the worst pandemic in memory, it was estimated that about 50 million people died, about 3% of the world's population (1.6 billion at the time). 500 million, or 1/3 were infected.
  • This slide the original of which was developed by the United States CDC illustrates the theoretical aims of community mitigation by public health measures, mass use of antivirals etc. However it needs to be appreciated that the effectiveness of PHM is by no means certain. A further discussion of this can be found through the ECDC PHM ‘Menu’ http://ecdc.europa.eu/en/Health_Topics/Pandemic_Influenza/phm.aspx
  • More than 99.9% of the emitted virus are in non-respirable particles, which settle within several feet of the infector. Highlights limited info on… the relative infectivity of influenza virus at different sites with virus receptors (e.g., the nasopharyngeal region vs. the alveolar region); the inactivation rate of influenza virus on environmental surfaces, including the hands; the surface-to-hand and hand-to- surface transfer efficiencies of influenza A virus; and the fraction of influenza virus depositing on facial membranes (eyes, nostrils, and lips) that reaches internal sites with virus receptors.
  • Fit-tested
  • Gawn – FFP3 Enunger – N95 (FFP2) / N99(FFP3)
  • Cowling – 272 to 12 studies 6 in health care settings – all small – none with any significant reduction in risk 4 in community settings – no difference in most studies – just one where if intervention within 36 hrs (Cowling study) Jefferson – 2958 to 58 studies (wider than just respirators) Only a small number of studies relevant to respirators / facemasks
  • What did we learn from the Influenza pandemic?

    1. 1. What did we learn from the influenza pandemic of 2009/10? John Cherrie
    2. 2. Summary… <ul><li>Pandemic, what pandemic! </li></ul><ul><li>Exposure routes and models </li></ul><ul><li>Respiratory protection and other risk management measures </li></ul><ul><li>What did we learn? </li></ul>
    3. 4. The pandemic… http://www.who.int/
    4. 5. Fatalities in the EU… Total 2876 UK 457 http://ecdc.europa.eu/en/healthtopics/Pages/Pandemic_Influenza.aspx
    5. 7. Aims of community intervention <ul><li>Delay and flatten epidemic peak. </li></ul><ul><li>Reduce peak burden on healthcare system and threat. </li></ul><ul><li>Somewhat reduce total number of cases. </li></ul><ul><li>Buy a little time. </li></ul>Daily cases Days since first case No intervention Based on an original graph developed by the US CDC, Atlanta With interventions
    6. 8. Exposure routes… <ul><li>Inhalation of airborne droplets </li></ul><ul><ul><li>Respirable or Inhalable size </li></ul></ul><ul><li>Hand-to-mouth or object to mouth transmission </li></ul><ul><ul><li>Mostly from inhalable or non-inhalable droplets </li></ul></ul><ul><li>Direct spray from a cough or sneeze </li></ul><ul><ul><li>Non-inhalable droplets </li></ul></ul>
    7. 9. Exposure models… Nicas and Jones. Relative contributions of four exposure pathways to influenza infection risk. Risk Analysis (2009) vol. 29 (9) pp. 1292-1303 Nicas and Jones. Relative contributions of four exposure pathways to influenza infection risk. Risk Analysis (2009) vol. 29 (9) pp. 1292-1303
    8. 10. Relative contribution of different pathways Nicas and Jones. Relative contributions of four exposure pathways to influenza infection risk. Risk Analysis (2009) vol. 29 (9) pp. 1292-1303
    9. 11. Official guidance… <ul><li>Standard infection control precautions and droplet precautions must be used for patients with suspected or confirmed pandemic influenza. </li></ul><ul><li>Good hand hygiene among staff and patients is an important control measure. </li></ul><ul><li>Good respiratory hygiene is essential: ‘Catch it, bin it, kill it’ </li></ul><ul><li>The use of PPE should be proportionate to the risk of contact with respiratory secretions and other body fluids, and should depend on the type of work or procedure. </li></ul><ul><li>FFP3 respirators should be used during potentially infectious aerosol generating procedures. </li></ul>http://www.hpa.org.uk/
    10. 12. 1918
    11. 13. Effectiveness of masks in lab tests… Study Design Conclusions Gawn et al Challenge test on test subject - Spray aerosol (<1μm to >200μm with approximately 50% of the particle number distribution <20μm) Surgical masks provide around a 6-fold reduction in exposure. Properly fitted respirators could provide at least a 100-fold reduction. Eninger et al Challenge test on dummy head - Aerosol only Penetration of aerosol about 3.5% (PF=30)
    12. 14. Respiratory protection… Study Design Conclusions Aiello et al 1437 young adults living in university residence halls during the 2006–2007 influenza season was designed. Residence halls were randomly assigned to 1 of 3 groups— face mask use, face masks with hand hygiene, or control— for 6 weeks. Neither face mask use and hand hygiene nor face mask use alone was associated with a significant reduction in the rate Cowling et al Systematic review There is some evidence to support the wearing of masks or respirators during illness to protect others, and public health emphasis on mask wearing during illness may help to reduce influenza virus transmission. There are fewer data to support the use of masks or respirators to prevent becoming infected. Loeb et al A randomized control trial to compare the surgical mask with the N95 respirator in protecting health care workers against influenza. Among nurses in Ontario tertiary care hospitals, use of a surgical mask compared with an N95 respirator resulted in non inferior rates of laboratory- confirmed influenza. Maclntyre et al Prospective cluster-randomized trial comparing surgical masks, non–fit- tested P2 masks, and no masks in prevention of influenza- like illness (ILI) in households. Concluded that household use of face masks is associated with low adherence and is ineffective for controlling seasonal respiratory disease. However, during a severe pandemic when use of face masks might be greater, pandemic transmission in households could be reduced. Jacobs et al Health care workers in a tertiary care hospital in Japan were randomized into 2 groups: 1 that wore face masks and 1 that did not. No difference in flu symptoms but statistically significant increase in “feeling bad” and headaches amongst those wearing masks. Jefferson et al Review systematically the evidence of effectiveness of physical interventions to interrupt or reduce the spread of respiratory viruses. Hand washing more than 10 times daily (odds ratio 0.45) Wearing masks (0.32), Wearing N95 masks (0.09), Wearing gloves (0.43), Wearing gowns (0.23), and Hand washing, masks, gloves, and gowns combined (0.09). Cowling et al Cluster randomized, controlled trial. 07 people presenting to outpatient clinics with influenza- like illness who were positive for influenza A or B virus by rapid testing (index patients) and 794 household members (contacts) in 259 households. Interventions implemented within 36 hours of symptom onset in the index patient, transmission of RT-PCR–confirmed infection seemed reduced, an effect attributable to fewer infections among participants using facemasks plus hand hygiene (adjusted odds ratio, 0.33 [95% CI, 0.13 to 0.87]) Study Design Conclusions Aiello et al 1437 young adults living in university residence halls during the 2006–2007 influenza season was designed. Residence halls were randomly assigned to 1 of 3 groups— face mask use, face masks with hand hygiene, or control— for 6 weeks. Neither face mask use and hand hygiene nor face mask use alone was associated with a significant reduction in the rate Cowling et al Systematic review There is some evidence to support the wearing of masks or respirators during illness to protect others, and public health emphasis on mask wearing during illness may help to reduce influenza virus transmission. There are fewer data to support the use of masks or respirators to prevent becoming infected. Loeb et al A randomized control trial to compare the surgical mask with the N95 respirator in protecting health care workers. Use of a surgical mask compared with an N95 respirator resulted in non inferior rates of laboratory- confirmed influenza. Maclntyre et al Prospective cluster-randomized trial comparing surgical masks, non–fit- tested P2 masks, and no masks in prevention of influenza- like illness (ILI) in households. Concluded that household use of face masks is associated with low adherence and is ineffective for controlling seasonal respiratory disease. However, during a severe pandemic when use of face masks might be greater, pandemic transmission in households could be reduced. Jacobs et al Health care workers in a tertiary care hospital in Japan were randomized into 2 groups: 1 that wore face masks and 1 that did not. No difference in flu symptoms but statistically significant increase in “feeling bad” and headaches amongst those wearing masks. Jefferson et al Review systematically the evidence of effectiveness of physical interventions to interrupt or reduce the spread of respiratory viruses. Hand washing more than 10 times daily (odds ratio 0.45) Wearing masks (0.32), Wearing N95 masks (0.09), Wearing gloves (0.43), Wearing gowns (0.23), and Hand washing, masks, gloves, and gowns combined (0.09). Cowling et al Cluster randomized, controlled trial. 07 people presenting to outpatient clinics with influenza- like illness who were positive for influenza A or B virus by rapid testing (index patients) and 794 household members (contacts) in 259 households. Interventions implemented within 36 hours of symptom onset in the index patient, transmission of RT-PCR–confirmed infection seemed reduced, an effect attributable to fewer infections among participants using facemasks plus hand hygiene (adjusted odds ratio, 0.33 [95% CI, 0.13 to 0.87])
    13. 15. So what did we learn? <ul><li>The importance of the respiratory pathway may have been underestimated </li></ul><ul><li>The effectiveness of interventions depends on prompt and consistent implementation </li></ul><ul><li>Surgical masks offer some protection, but you probably need a respirator to protect against aerosols </li></ul><ul><li>Occupational hygiene has a lot to contribute to understanding how best to manage infectious diseases </li></ul>
    14. 16. Slide presentation on OH-world.org You can download this and other presentations from OH-world.org Follow my blog on Twitter.com/JohnCherrie

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