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Infection used to be one of the biggest killers in hospitals before modern hygiene standards were introduced. But the risk of infection hasn't gone away.

Hospital infection has been an issue for as long as there have been hospitals. Putting so many weak and vulnerable people in close proximity, many of them arriving with contagious diseases is bound to encourage the spread of infection.

Electron micrograph of salmonella bacteria on a cell Wellcome Collection, CC-BY
Salmonella enterica bacteria on a cell has induced ruffling on the cell membrane triggered by secreted bacterial proteins.

What is an infection?

An infection happens when infectious agents (commonly called germs) enters the body and begin to reproduce and spread, releasing toxins into the blood and disrupting bodily functions. The infectious agents are simple micro-organisms such as bacteria, viruses, fungi, and prions.

How an infection spreads depends on the type of micro-organism. Infection can be transmitted in a variety of ways, including:

  • skin contact
  • bodily fluids
  • contact with faeces
  • airborne droplets or particles
  • touching an object that an infected person has also touched.


Some infections, such as cold viruses, are mild and little more than a nuisance, but others are severe and life-threatening. The body’s immune system usually protects the body against infections, but if the infection spreads too rapidly or cannot be controlled, the immune system may be overwhelmed and the infection may become dangerous. 

The common symptoms of infection are triggered by the immune systems response to an infecting micro-organism and include fever, feeling cold or shivery, localised redness, swelling or discharge of pus, nasal congestion, coughing, diarrhoea or vomiting. These are all signs that the body is trying to rid itself of the infection.

Hospital infections

In the past, even when an operation or treatment was successful, the patient often died from infection. Infections in hospital wards, particularly after surgery, were so common that the phenomenon was known as hospitalism or ward fever.

A man in a hospital bed with gangrene in his amputated arm Wellcome Collection, CC-BY
An American Civil War soldier with hospital gangrene of an arm stump (1861-65)

Inexplicably, an infection might sweep through an entire ward, killing the most vulnerable. No wonder surgery was a last resort for most patients. Victorian surgeon James Y. Simpson, the discoverer of chloroform, claimed that:

a man laid on the operating table in one or our surgical hospitals is exposed to more chance of death than was the English soldier on the field of Waterloo.

As early as 1847, the Hungarian doctor Ignaz Semmelweis  had realised that infection rates were far worse in maternity wards attended by doctors than in wards where midwives only delivered the babies. Doctors and medical students handled a wider variety of patients as well as dead bodies, whereas midwives only came into contact with generally healthy pregnant women.

Sketch of a woman in early stages of puerperal fever Wellcome Collection, CC-BY
A woman who developed puerperal fever, one of the most common childbirth infections, three days after giving birth, 1843.

Semmelweis suspected that it was the doctors who were bringing the infections into the ward. He introduced a simple antiseptic hand-washing procedure for medical staff entering his wards and found the infection rates fell.

The infections were being transferred from patient to patient by unwitting doctors, who rarely washed their own hands or instruments between procedures. But because no one knew what caused infections, Semmelweis couldn't prove that hand-washing prevented the spread of infection and his findings were not widely adopted. Tragically Semmelweis himself died from blood poisoning caused by a cut on his finger.

The germ theory of disease

The French scientist Louis Pasteur speculated that the spread of microorganisms (called germs) in the body could explain infectious disease. This became known as the germ theory of disease. Although he never tested the theory, Pasteur suggested that germ-killing chemicals might be able to limit the spread of infections.

Scientist Louis Pasteur at work in his laboratory, 1885. Wellcome Collection, CC-BY
Scientist Louis Pasteur at work in his laboratory, 1885.

In the UK, surgeon Joseph Lister had been investigating surgical infection and was inspired by Pasteur’s research. Lister develop the antisepsis system in order to prevent infections from entering a wound during and after surgery. 

Lister's system killed infectious agents using carbolic acid as a disinfectant for washing the hands, cleaning surgical instruments and on post-surgical dressings.

an operation using the antisepsis system with carbolic spray Wellcome Collection
An operation using the antisepsis system, as well as disinfecting hands and instruments, a carbolic spray disinfects the air.

Lister published a paper about his system in the Lancet, but because Pasteur’s germ theory was still untested many surgeons were sceptical. Without the belief that germs were real and dangerous, many surgeons found the antiseptic system unnecessarily complicated and excessive.

Some surgeons were opposed because they thought that Lister was proposing carbolic acid as a treatment for infection rather than as one possible chemical barrier or antiseptic for preventing infection entering the body. They objected that carbolic acid was too toxic for wound dressings because, in strong solutions it irritated and burned the wound and surrounding skin, and an overdose could cause excessive vomiting.

The importance of hospital sanitation

Some of Lister’s critics argued that good hygiene and cleanliness were all that was needed to control infection, and that Lister’s elaborate antisepsis system was simply another form of sanitation.

Lister responded by producing statistical evidence from his wards at Glasgow Infirmary to demonstrate the effectiveness of the antisepsis system, but his data was limited and failed to convince many of his critics. Most surgeons preferred to wait until there was stronger evidence for the germ theory and antisepsis before committing themselves.

But one person who did convince hospital administrators about the importance of preventing hospital infection was Florence Nightingale. She used statistical evidence based on the data she gathered at military hospitals hospitals during the Crimean War to demonstrate that infections, not war wounds, were the biggest killers of soldiers in army hospitals.

When Nightingale returned to Britain, she collaborated with the epidemiologist William Farr in the preparation of hospital statistics for her book Notes on Hospitals (1859).

Florence Nightigale's statistical chart showing causes of mortality in the army of the East, 1858. Wellcome Collection, CC-BY
Florence Nightigale's statistical chart showing causes of mortality in the army of the East, 1858.

The compelling statistical evidence she provided convinced many hospitals that improved sanitation was sufficient to reduce infection-related deaths and diseases in hospitals.

Like many doctors at the time, Nightingale believed in the traditional view that miasmas (bad air) and not germs spread infection. Her campaign was based on empirical evidence rather than scientific proof.

Nevertheless, her campaign to clean up hospitals improved standards of care as well as hygiene and led to fewer deaths from infection. She also set up a training school in London, where nurses were instructed the principles of good hygiene. 

Florence Nightingale with trainee nurses from St Thomas's Hospital London
Florence Nightingale with her graduating class of nurses from St Thomas' Hospital, 1886.

Lister didn’t think that sanitation was important if proper antiseptic procedures were in place. His sanitary procedure in the operating room simply consisted of removing his coat, rolling up his sleeves and pinning a clean but unsterilised towel over his waistcoat and trousers.

Such was his faith in germ theory and antisepsis that cleanliness seemed irrelevant to him. In an address to the British Medical Association he declared:

My patients have the dirtiest wounds and sores in the world’ but, he explained, ‘aesthetically they are dirty, though surgically they are clean.

In fact both good hygiene and antiseptic procedures are needed to prevent and control hospial infection. Both the sanitarians and the Listerians had yet to be convinced by each other's evidence.

Modern infection control

In 1877 the German scientist Robert Koch provided convincing scientific evidence that germs were the cause of infectious diseases such as anthrax and typhoid. His laboratory work on bacterial infection also showed that dry heat and steam sterilisation were as effective as chemical agents in controlling and preventing the growth of bacteria.

Lister's antisepsis, Nightingale's hospital hygiene and Koch's bateriology combined in a new approach to infection control in hospitals, which was called asepsis. In modern hospitals asepsis is the norm, combining steam sterilisation of instruments and clothing in the operating theatre with disinfectant cleaning of surfaces and antiseptic cleaning and dressings for wounds.

A laboratory sterilising room with large autoclave. Wellcome Collection, CC-BY
A laboratory sterilisation room with a large autoclave for steam sterilisation on the right.

The discovery of antibiotics in the 1940s made a dramatic difference to the control of infections in the body. For the first time, there was an effective drug treatment and cure for infections.

Gradually, hospitals became complacent about hygiene standards. Why would you put so much effort into preventing infections when you could just focus on treating the infected patient? 

Unfortunately, bacteria and viruses evolve at astonishing rates, and some strains of 'superbugs' have become resistant to antibiotics. Overuse of antibiotics has, once again, made hospital infection potentially life-threatening. 

Electron micrograph of a cluster of mrsa bacteria Annie Cavanagh/Wellcome Collection, CC-BY 4.0
Clusters of methicillin-resistant Staphylococcus aureus (MRSA) bacteria. Colour enhanced electron micrograph

Antibiotic resistant 'superbugs' such as MRSA exist inside and outside hospitals so modern health care services have to be vigilant about infections in the hospital and those brought in by visitors. Hospital infection was almost thought of as a thing of the past, but it has not gone away, and hygiene and aseptic controls are as important as ever.

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