Staphylococcal infections are a group of different infections that are caused by staphylococcus bacteria.
There are several types of staphylococcus bacteria, but most infections are caused by a type called staphylococcus aureus (S. aureus).
Staphylococcal aureus
S. aureus is common in humans. It is often found inside the nose and on the surface of the armpits and buttocks. In most cases, the bacteria do not cause any symptoms. If a person has bacteria living on their body but they do not experience any symptoms, they are said to be colonised by bacteria.
It is estimated that 80% of all people will be colonised by S. aureus at least once in their life, and that 20-30% are persistently colonised.
Types of staphylococcal infections
The different types of staphylococcal infections can be broadly classified into two groups:
- skin infections, such as boils or impetigo (a skin infection that causes the skin to become crusty and itchy)
- invasive infections, such as blood poisoning or endocarditis (an infection of the heart’s lining)
Skin infections usually occur when the S. aureus bacteria invade a cut in the skin.
Invasive infections can develop as a complication of a skin infection that has spread beyond the skin due to a person having a weakened immune system. Invasive infections can also occur from using medical equipment that goes inside the body, such as a feeding tube or catheter (a tube that is used to empty the bladder).
Food poisoning can occur if you eat food that is contaminated with S. aureus bacteria. Food poisoning usually occurs as a result of eating food, usually meat, that either has not been cooked properly or has not been chilled at the right temperature.
How common are staphylococcal infections?
Staphylococcal skin infections are very common, particularly among children, teenagers and young adults. This may be because at a young age, the immune system is still underdeveloped. Impetigo, for example, accounts for 10% of all reported skin conditions in children.
Invasive staphylococcal infections are less common than skin infections, but they are much more serious. This is because once the bacteria penetrate the skin and enter the blood or organs, they can rapidly multiply and release toxins which can cause multiple organ failure and a massive drop in blood pressure. This is a serious complication of infection, which is known as sepsis.
Endocarditis is a very serious condition because it can lead to heart failure. It is estimated that for every 100,000 people, 30 will develop an invasive infection in any given year.
Antibiotic resistance
One of the biggest challenges in treating staphylococcal infections is that many strains of the S. aureus bacteria have developed resistance against a number of different antibiotics.
These bacteria are known as meticillin-resistant staphylococcus aureus (MRSA). Meticillin is a type of antibiotic. However, the term is slightly misleading because MRSA is also resistant to other antibiotics as well.
MRSA can cause more severe infections and needs to be treated with an injection of a powerful antibiotic called vancomycin.
The obvious worry is that certain strains of bacteria will begin to develop a resistance to vancomycin. So far, there has only been a handful of reported cases of vancomycin-resistant staphylococcus aureus, although this figure could increase in the future.
As a result of the dangers posed by antibiotic resistance, there has been a shift in the way doctors prescribe antibiotics. Rather than prescribing them in cases where they may be of some benefit, such as for a mild chest infection, antibiotics are now only prescribed when then is a clear clinical need for them.
Outlook
The outlook for staphylococcal skin infections is generally good. Most infections are mild and quickly respond to treatment with antibiotics.
The outlook for people with invasive staphylococcal infections will depend on a number of factors such as:
- the person’s age
- where in the body the infection has spread to
- whether the infection is being caused by MRSA or ‘standard’ S. aureus bacteria
- whether the person has any pre-existing health conditions, such as heart disease
Depending on the above risk factors, the outlook for invasive staphylococcal infections can range from moderately good to poor, with an estimated mortality of 3%-80%.
Glossary
Bacteria
Bacteria are tiny, single-celled organisms that live in the body. Some can cause illness and disease and some others are good for you.
Heart
The heart is a muscular organ that pumps blood around the body.
Tissues
Body tissue is made up of groups of cells that perform a specific job, such as protecting the body against infection, producing movement or storing fat.