Bioaerosol production on a respiratory ward
Although much hospital acquired infection is associated with person-to-person contact, there is increasing evidence that some nosocomial infections may be transmitted via the airborne route. However, the knowledge base concerning airborne micro flora in hospitals is poor. In particular, there is a need for good quality data relating bioaerosol production to clinical activity in hospital wards. A short aerobiological survey was therefore undertaken by the authors on a respiratory ward at St James's University Hospital in Leeds in order to gain an understanding of the relationship between activity and bioaerosol production. This survey involved regular microbiological and particulate (0.3 – 5 µm) sampling of the ward air, together with an observational study of ward activity. Two identical four bedded ward bays were surveyed, one containing high dependency patients who regularly used non-invasive ventilators (NIVs), and the other containing patients who did not require mechanical ventilation.
Methodology
Observations
For both bays, ward activity was observed from 9.00 to 17.00, and the movements of patients, nurses, doctors, visitors, cleaners and other workers recorded. Regular microbiological and particulate samples were taken from the air throughout the study period. The air sampling points were located near the window in each bay, as shown in Figure 1.
Figure 1 Plan of a four bedded study bay.
Microbiological and Particulate Air Sampling 
The number and size distribution of airborne particulate matter on the wards was recorded using a Kanomax 3886 laser particle counter (Kanomax, Andover, NJ, USA) which recorded the particle count every five minutes for five size distributions, 0.3 - 0.5µm, 0.5 - 1µm, 1 - 3µm, 3 - 5µm and >5µm. Microbial air sampling was undertaken using a single stage Microbio MB2 impactor (FW Parrett Ltd, London , UK ).
Results
Figure 1 and 2 below show the particle counts in the bays with the major activities highlighted. Figures 3 and 4 show the total viable counts collected 3 times every 30mins, again with the main activities in the ward shown.
A = Breakfast, ward round and bed
making (Bed B), B = Patient B using NIV
C = Patient B using NIV, D = Bed making (Bed D) and cleaning
E = Furniture moved, floor mopping and bed making (Beds B, C
& D)
F = Lunch time and drugs round, G = Visitor adjacent to
particulate counter
H = Patients C and D using nebulizers,
I = Beds A and C made and bed C disinfected ready for new
patient
J = Activity around patient B, curtains close, K = Evening
meal
Figure 1 Airborne particulate count in the HD bay on the 16 th December 2004
(logarithmic scale)
A = Breakfast and bed making, B =
Ward round, C = Patient B using nebulizer
D = Floor mopping, E = Patient C washing, F = Bed making
G = Lunch time, H = Patients C and D using nebulizers, I =
Activity at bed B
J = Patients using nebulizers, K = Tea trolley round,
L = Visitor adjacent to particle counter, M = Evening meal
Figure 2 Airborne particulate count in the non-HD bay on the 17 th December 2004
(logarithmic scale)
A = Bed making at bed B, B = Bed
making at bed B, C = Bed making at bed C
D = Bed making at bed D, E = Bed making at bed B, F = Meal trays
dispensed
G = Meal trays collected, H = Patients using nebulizers, I = Bed
making at beds A and C
J = New patient in bed C and furniture moved, K = Activity around
bed B
Figure 3 Airborne microbial count in the HD bay on the 16 th December 2004
A = Breakfast and bed making, B =
Patient C washing, C = Activity around bed B
D = Meal trolley outside entrance to bay, E = Patients C and D
using nebulizers,
F = Waste bins changed
Figure 4 Airborne microbial count in the non-HD bay on the 17 th December 2004
Conclusions
The survey found a correlation between activity and aerosol production. The study demonstrated that aerosol particles (including bioaerosol particles) are frequently liberated within the clinical environment. It also demonstrated that it is possible to link aerosol production with specific tasks, using the methodology described. The use of nebulizers appears to be associated with the production of <3 µm particles, whereas the movement of people and bed making is more likely to be associated with the production of >3 µm particles.