Thursday, October 11, 2012

The Flight Of The Bacterial Intruder





# 6625


HCAIs (Health care associated Infections) or HAIs (Hospital acquired infections) constitute a major threat to life, health, and the cost of medical care in this country, and around the world. This oft quoted assessment from the CDC on the burden of Hospital Acquired Infections in the United States is from 2010.


A new report from CDC updates previous estimates of healthcare-associated infections. In American hospitals alone, healthcare-associated infections account for an estimated 1.7 million infections and 99,000 associated deaths each year. Of these infections:

  • 32 percent of all healthcare-associated infection are urinary tract infections
  • 22 percent are surgical site infections
  • 15 percent are pneumonia (lung infections)
  • 14 percent are bloodstream infections


A 2009 report The Direct Medical Costs of Healthcare-associated Infections in U.S. Hospitals and the Benefits of Prevention finds:


Applying two different Consumer Price Index
(CPI) adjustments to account for the rate of inflation in hospital resource prices, the overall annual direct medical costs of HAI to U.S. hospitals ranges from $28.4 to $33.8 billion (after adjusting to 2007 dollars using the CPI for all urban consumers) and $35.7 billion to $45 billion (after adjusting to 2007 dollars using the CPI for inpatient hospital services).



As you can imagine, hospitals are engaged in a perpetual battle against the spread of infection - and while progress is being made - many pathogens continue to slip past the infection control safeguards.


A study from the University of Leeds recently published in the Journal Building and Environment may provide a clue as to why the infection control measures being used today have failed to curb the spread of bacteria in the hospital setting.



Bioaerosol Deposition in Single and Two-Bed Hospital Rooms: A Numerical and Experimental Study

M.F. King, C.J. Noakes, P.A. Sleigh, M.A. Camargo-Valero


You’ll find the abstract, along with figures and tables from this article, at the link above. But the full paper is behind a pay wall. The University of Leeds website, however, has a synopsis of this research project, which is excerpted below:.



Superbugs ride air currents around hospital wards

Published Thursday 11th October 12

Hospital superbugs can float on air currents and contaminate surfaces far from infected patients’ beds, according to University of Leeds researchers.


The results of the study, which was funded by the Engineering and Physical Sciences Research Council (EPSRC), may explain why, despite strict cleaning regimes and hygiene controls, some hospitals still struggle to prevent bacteria moving from patient to patient.


It is already recognised that hospital superbugs, such as MRSA and C-difficile, can be spread through contact. Patients, visitors or even hospital staff can inadvertently touch surfaces contaminated with bacteria and then pass the infection on to others, resulting in a great stress in hospitals on keeping hands and surfaces clean.


But the University of Leeds research showed that coughing, sneezing or simply shaking the bedclothes can send superbugs into flight, allowing them to contaminate recently-cleaned surfaces.


PhD student Marco-Felipe King used a biological aerosol chamber, one of a handful in the world, to replicate conditions in one- and two-bedded hospital rooms. He released tiny aerosol droplets containing Staphyloccus aureus, a bacteria related to MRSA, from a heated mannequin simulating the heat emitted by a human body. He placed open Petri dishes where other patients’ beds, bedside tables, chairs and washbasins might be and then checked where the bacteria landed and grew.


The results confirmed that contamination can spread to surfaces across a ward. “The level of contamination immediately around the patient’s bed was high but you would expect that. Hospitals keep beds clean and disinfect the tables and surfaces next to beds,” said Dr Cath Noakes, from the University’s School of Civil Engineering, who supervised the work. “However, we also captured significant quantities of bacteria right across the room, up to 3.5 metres away and especially along the route of the airflows in the room.”


“We now need to find out whether this airborne dispersion is an important route of spreading infection,” added co-supervisor Dr Andy Sleigh.

(Continue . . .)



While we often think first of viruses when it comes to airborne transmission of illness, some types of bacteria (e.g. Legionella, Mycoplasma pneumonia, Tuberculosis) are easily aerosolized and transmitted.


This study is not the first to identify the airborne spread of Staphylococcus aureus, but they have developed an ingenious way to quantify it.


Regarding MRSA and C. Difficile the Journal of The Royal Society published a review in 2009 called:


Airborne transmission of disease in hospitals

I. Eames, J. W. Tang,Y. Li and P. Wilson


MRSA can survive on surfaces or skin scales for up to 80 days and spores of Clostridium difficile may last even longer. MRSA can be transmitted in aerosol from the respiratory tract but commonly attaches to skin scales of various sizes. The distance of travel depends on the size of the scale, the larger falling to the floor within 1–2 m, the smaller travelling the entire length of the ward.


Clostridium difficile spores are thought to spread in the air and can be found near a patient carrying the organism (Roberts et al. 2008). However, unlike MRSA, they are rarely isolated from air samples.



Not surprisingly, in 2010, we saw a study published in the AJIC: American Journal of Infection Control that found that the more roommates you have during a hospital stay, the greater chance you will have of contracting an HAI like MRSA or C. Diff.


Exposure to hospital roommates as a risk factor for health care–associated infection

Meghan Hamel, MSc, Dick Zoutman, MD, FRCPC, Chris O'Callaghan, DVM, MSc, PhD


The authors used this study to promote the idea  of making private (or at least, semi-private) rooms the norm in Canadian hospitals. While acknowledging that it would involve considerable up-front costs, they believe the long-term savings would be considerable.


All of this highlights the great challenges involved in substantially reducing the incidence of HAIs in our health care facilities.


Solutions must not only include stringent hand hygiene and improved cleaning methods, but engineering solutions as well.


For more on the prevention of Hospital Acquired Infections you may wish to visit the CDC’s HAI PAGE.




Or revisit some of these earlier blogs on hospital acquired infections.


HPA: Healthcare-Associated Infection (HCAI) Survey
A Barrier To Good Hand Hygiene
Study: Hospital Uniforms And Bacteria
Study: HAIs, Universal Surveillance, & MRSA


And finally, the subject of HAIs is often addressed by Maryn McKenna on her excellent Superbug Blog, and was a major focus of her book SUPERBUG: The Fatal Menace Of MRSA.


Both are highly recommended.

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