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Madeleine McPherson. RN. MACN Infection Prevention and Control Consultant

    The normal human body is host to trillions of microbes. All are acting as a part of our normal defence mechanism against possible invaders.

Number varies between 4000 and 400,000 in each square centimetre of our skin and mucous membrane which, if stretched out covers 8 tennis courts!!!!!!.

Staphylococcus aureus (

golden staph) is one of those found on the skin and in moist areas of 50% of healthy individuals.

The number of bacteria on the bowel equals the number of people who have ever inhabited this planet.

     We do not live in a sterile world, thank goodness.

Microbes are the most numerous living thing on earth. They are all around us. Nearly all of them function to break down the bodies of plants and animals after they have died, to release vital nutrients that are used again.

Only a few are able to attack their larger neighbours while they are still alive, to cause disease.

To cause an infection the microbes must come in sufficient numbers and be able to reach a susceptible site.

  In the early days of microbiology, a simple Bacteriologists found that Streptococci , exposed to the air, after being shed from the body of a person with an infection, suffer from progressive damage before they die.

In this pre-morbid state, they can still be detected in the laboratory, but they have lost their virulence.

Meers, McPherson, Sedgwick,. Infection Control in Healthcare (2000)

    1976 An epidemic of respiratory disease occurred during an American Legion convention in Philadelphia which resulted in 220 hospitalisations and 34 deaths.

L. pneumophila

were all staying.

was present in the air conditioning system of the hotel where they Subsequent epidemics have occurred in hotels hospitals, cruise liners, shopping centres etc.

    A slow growing gram negative rod-shaped organism.

L pnemophila

multiples inside amoebae that inhabit the same ecological niche.

The ecological niche must provide the right temperature, plenty of organic matter and a vehicle of infection.

Severe legionellosis is seen in individuals predisposed to smoking, chronic lung disease alcoholism, old age and immunosuppressant.

   Legionella is an example of wholly environmental infection when the causative microbe may not be derived from a living thing.

There are many members of the genus but over two thirds of human infections are caused by

L.pneumophia serotype 1.

Another common species is

Legionella Longbeachie

which is found in potting mix.

    Survives and multiples in water including rivers, lakes, streams.

Airborne dispersal may occur when aerosols are created.

Temperature dependant. Prefers between 60 0 and 20 0 .

Insensitive to pH.

     Does not pass from person to person.

Acquired from contaminated droplets.

Found in poorly maintained air conditioners, shower heads, mixer taps.

Control. Showers and taps that are not frequently used should be flushed through weekly for 5 minutes.

Thermostat mixing valves should be cleaned and serviced quarterly.

Source Route of transmission Port of Entry Incubation period Infection

    The immune system in the host becomes important.

To cause an infection, a microbe must have come from somewhere ‘source of infection’.

Finds a port of exit to escape from the source and needs a ‘vector’ or vehicle of infection to conduct an ID along a pathway to reach a ‘portal of entry.

Legionnela a very good example. Aerosol transmission and a susceptible host (Legionnaires)

    A place in which ‘infecting’ microbes can be found.

All microbes require transport. Example Semmelweis.

No doubt contaminated the walls, floors, bedding, furniture and air were heavily contaminated with streptococci, yet hand washing on its own reduced infection rates from 10%-1%.

 Renamed – Healthcare Associated Infections.

  Facts: 75% of all HAI are self infections.

24% cross infection.

<1% equipment.

The focus on equipment control could be said to be out of proportion to their overall significance.

 Note: Since we were born, our hands have been used to sample the environment. Where they end up is very important in the health care setting: HAND WASHING IS THE SINGLE MOST IMPORTANT MEASURE IN THE PREVENTION OF INFECTION.


 Transient flora.

the environment) Microorganisms isolated from the skin that are not usually present. (derived from contact with previous patient of  Resident flora.

Microorganisms that permanently reside on the skin.

 After an aseptic hand wash, the hands could be recontaminated via the tap.

    Hand basins must be readily available and their use encouraged The modern trend to alcohol rubs is not always a substitute for soap and water.

The water flow must not be over the outlet. (millions of microbes in the drain doing no harm until they are given help, e.g. Splashing) The hand basins also designed not to permit splashes.

    In areas where asepsis is required (ORs, Procedure rooms etc) elbow taps are required. (foot taps have problems). In areas where antisepsis is required, wrist taps are acceptable.

Sensor taps excellent if they can be guaranteed.

Hand taps in all other areas

    Hungarian appointed to the Obstetric Division of the Vienna General Hospital.

Comprised two clinics. Medical students in one and trainee midwives in the other.

Maternal death rate significantly higher in the first clinic. 10% as to 3%.

Semmelweis, worried, investigated.

    Semmelweis.

No doubt contaminated the walls, floors, bedding, furniture and air were heavily contaminated with streptococci, yet handwashing on its own reduced infection rates from 10%-1%.

Streptococci still causes serious newsworthy sepsis.

Innovative medically acquired and opportunistic pathogen.

     Infection Control must be based on science.

Rituals are an expensive, ridiculous waste of time.

Know your policies, they are based on science.

Monitor and recognise changing patterns.

Question the questionable.