Infection prevention and control
Introduced| English | Meaning |
|---|---|
| standard precautions | Infection-control measures, such as hand hygiene and gloves, used with every patient. |
| cleaning/ˈkliːnɪŋ/ | cleaning |
| disinfection | disinfection |
| sterilisation | Killing all microbes, including spores, on an item. |
The cheapest infection
- In 1847 Ignaz Semmelweis made doctors wash their hands in chlorine before delivering babies. Deaths from childbed fever on his ward fell from about 10% to about 1–2%.
- Prevention is the chain of infection, cut on purpose. The cheapest infection is the one that never happens.
Standard precautions
- Standard precautions 标准预防 apply to every patient: hand hygiene, gloves when contact with body fluids is expected, and safe handling of needles.
- The reservoir is often a patient who looks well, so standard precautions are never optional.
Precautions matched to the route
- Contact precautions add gloves, a gown and a single room. Droplet precautions add a mask within 1–2 m.
- Airborne precautions add a fitted respirator and a negative-pressure room, which keeps air flowing into the room, not out.
Match each situation to the precaution it needs.
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Standard precautions always, plus the level that matches the route.
The physics of the route
- Droplets larger than about 5 µm fall within about 1–2 m, so distance and a mask break the chain.
- Particles of 5 µm or less stay in the air for hours and drift with air currents: measles, tuberculosis and chickenpox need airborne precautions. Influenza is managed with droplet precautions.
Why does tuberculosis need a fitted respirator rather than a surgical mask?
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Airborne particles of 5 µm or less drift for hours; only a sealed respirator filters them.
Cleaning, disinfection, sterilisation
- Cleaning 清洁 removes dirt; disinfection 消毒 kills most microbes but not bacterial spores; sterilisation 灭菌 (for example steam at 121–134 °C) kills everything.
- Match the level to the item: anything entering sterile tissue is sterilised; items touching mucosa are disinfected to a high level; items touching intact skin are cleaned.
Put the methods in order from weakest to strongest.
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Only sterilisation kills bacterial spores.
A surgical instrument will enter sterile tissue. What does it need?
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Anything entering sterile tissue must be free of all microbes, spores included.
Disinfection kills bacterial spores.
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Spores survive most disinfectants; only sterilisation reliably kills them.
Vaccinating the staff
- Staff meet every patient, so staff vaccination is herd immunity applied to the people at the centre of the ward's chain.
- The protected fraction is uptake × vaccine effectiveness; the rest stay susceptible.
Worked example: staff flu vaccination
- (Fictional) Staff uptake rises from 40% to 90%. With a vaccine that protected everyone, the susceptible fraction would fall from 60% to 10%, six-fold.
- With a vaccine that protects 60%: susceptible = $1 - 0.4 \times 0.6 = 76\%$ before and $1 - 0.9 \times 0.6 = 46\%$ after. Still a large gain, but smaller.
With a vaccine that protects everyone, staff uptake rises from 30% to 80%. By what factor does the susceptible fraction fall?
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Susceptible falls from 70% to 20%, and 70 ÷ 20 = 3.5.
Uptake is 80% and the vaccine protects 50% of those vaccinated. What percentage of staff remain susceptible?
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Protected = 0.8 × 0.5 = 40%, so 60% remain susceptible.
Worked example: the surgical cluster
- (Fictional) Three wound infections with the same S. aureus appear on days 5–7 after surgery in one theatre.
- The timing points to the operation or the first two days of care. Then the chain: the reservoir (a carrier or the environment), the route (contact) and the way in (the wound).
Three common slips
- Skipping standard precautions for a patient who looks well. Carriers look well.
- Using droplet precautions for an airborne infection. Measles and tuberculosis need a respirator and a negative-pressure room.
- "Disinfected means sterile." Spores survive disinfection.
Recap
- Standard precautions for everyone; add contact, droplet or airborne precautions to match the route.
- Droplets (over 5 µm) fall within 1–2 m; airborne particles (5 µm or less) drift for hours.
- Cleaning < disinfection < sterilisation; staff protection = uptake × effectiveness.