University Hospital Southampton NHS Foundation Trust

EaSe: Environmental monitoring of airborne samples

The emergence of influenza A/H1N1 or ‘swine flu’ during the past year has caused concern for members of the public and health-care professionals alike. ‘Swine flu’ is a respiratory pathogen transmitted via small droplets expelled from the nose and mouth. The available epidemiological evidence suggests human to human transmission is generally limited to close interactions between an infected individual and a susceptible individual. In the hospital setting, certain medical procedures that health-care professionals may be required to undertake regularly on influenza infected individuals, have the potential to generate more of these small droplets. These procedures have been termed ‘aerosol generating procedures’ (AGPs) and it is suspected that these procedures may increase the risk of health-care workers (HCWs) and relatives contracting the infection. These procedures and processes are:

  • Intubation/extubation and conventional mechanical ventilation (IPPV)
  • Non invasive ventilation (NIV)
  • Bronchoscopy 
  • Nebulisation
  • High flow oxygen
  • High frequency oscillatory ventilation chest physiotherapy

We aim to study the role that these potential AGPs have in transmitting respiratory viruses and bacteria in hospitals in the close environment around patients with suspected or proven lower respiratory tract infections receiving IPPV or NIV. Environmental air samples will be taken in the area surrounding such patients in which aerosols generated by AGPs might be dispersed.

If influenza virus or other respiratory pathogens are detected in the air samples taken during or soon after potential AGPs have been performed, this will help inform the level of risk to HCWs and visiting relatives.  If certain procedures are found to pose a greater risk of generating aerosols than others this data will inform policies regarding the appropriate personal protective equipment (PPE) required for HCWs and relatives whilst in the vicinity of patients in whom these AGPs are being performed. This would benefit hospital staff, patients, visitors and ultimately the general public by interrupting an important mode of transmission.

When using aerosolised respiratory therapy, particle size determines the site of distribution in the airway.  The risk of infection from aerosols containing either viruses or bacteria generated by AGPs performed on patients with lower respiratory tract infections on an intensive care unit may be similarly determined.  It is assumed that droplets (as may be produced by a sneeze or a cough) and are greater than 10 µm in diameter are dispersed only to a radius of 1 metre, present little infective risk to those HCWs and relatives outside of this zone.

There is however no data to support this theory.  We aim to quantify the actual aerosol production associated with the designated AGPs defined above and to assess the pathogenic load and dispersion of droplets or aerosols generated.

Inclusion criteria

Children or adults on an intensive care unit with s suspected or proven lower respiratory tract infection defined as:

  • New chest X-Ray changes

And one or more of the following:

  • Central temperature > 380C (> 38.50C in children) or < 360C.
  • White blood cell count < 4000 cells/mm2 or > 12,000 cells/mm2, or the presence of > 10% immature neutrophils.
  • Positive microbiology or virology from respiratory secretions.
  • Mucopurulent secretions from the respiratory tract.