Staphylococcal infections

Page last reviewed: 13/07/2011

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.

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%.

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.

Page last reviewed: 13/07/2011

Staphylococcal skin infections

The symptoms of some common types of staphylococcal skin infections are outlined below.

Boils

Boils are painful, red bumps on the skin that usually occur on the neck, face, thighs, armpits and buttocks. They are usually caused by an infected hair follicle (a small sac in the skin that a hair grows out of).

As white blood cells fight the infection, pus forms inside the boil causing it to grow larger.

Eventually, the boil will rupture (burst) and the pus will drain away.

Impetigo

Impetigo is a highly contagious bacterial skin infection. There are two types of impetigo:

  • non-bullous impetigo, which causes sores that quickly rupture, leaving a yellow-brown crust
  • bullous impetigo, which causes large, painless, fluid-filled blisters

The sores and blisters that are caused by both types of impetigo are usually very itchy. However, it is important not to scratch them because doing so can spread the infection to other parts of the body.

Cellulitis

Cellulitis is a bacterial infection of the deep layer of skin (dermis) and the layer of fat and soft tissues (the subcutaneous tissues) that lie underneath the skin. The infection can make your skin red, swollen and painful.

Cellulitis can also make you feel generally unwell and cause symptoms such as:

  • a high temperature (fever) of 38C (100.4F) or above
  • nausea
  • shivering
  • chills

Staphylococcal food poisoning

The symptoms of staphylococcal food poisoning can develop between 30 minutes to eight hours after eating contaminated food. Common symptoms include:

  • abdominal cramps
  • nausea
  • vomiting

In some cases, these symptoms are followed by diarrhoea. The symptoms of staphylococcal food poisoning usually pass within 24 hours.

Invasive staphylococcal infections

The symptoms of some uncommon but serious invasive staphylococcal infections are described below.

Sepsis

The symptoms of sepsis (also known as blood poisoning) usually develop quickly and include:

  • a high temperature (fever) of 38C (100.4F) or above
  • fast heartbeat (tachycardia)
  • fast breathing
  • low blood pressure (hypotension), which will cause you to feel dizzy when you stand up
  • a change in mental behaviour, such as confusion or disorientation
  • diarrhoea
  • reduced urine flow
  • cold clammy skin
  • pale skin
  • loss of consciousness

Sepsis is a medical emergency. If you suspect that you or someone in your care is experiencing sepsis, dial 999 and ask for an ambulance.

Toxic shock syndrome

Toxic shock syndrome is a rare condition that is caused when S. aureus bacteria enter the bloodstream and begin to release toxins (poisons). Most people are immune to the effects of the toxins, but a minority are not. In these people, the toxins can cause a drop in blood pressure, as well as organ and tissue damage.

Symptoms of toxic shock syndrome include:

  • vomiting
  • a skin rash that looks like sunburn
  • diarrhoea
  • fainting, or feeling faint
  • muscle aches
  • dizziness
  • confusion

Septic arthritis

Septic arthritis is a condition where a joint becomes infected with the S. aureus bacteria. Symptoms of septic arthritis include:

  • joint pain and swelling
  • red and tender skin around the joint
  • a high temperature (fever) of 38C (100.4F) or above

Endocarditis

The symptoms of endocarditis (inflammation of the heart) can develop gradually over many weeks or quickly over a few days.

Symptoms include:

  • a high temperature (fever) of 38C (100.4F) or above
  • chills
  • sweating, including night sweats
  • muscular aches and pains
  • chest pain
  • coughs
  • weakness and fatigue
  • headache
  • shortness of breath
  • unexplained weight loss

Page last reviewed: 13/07/2011

Skin infections

Staphylococcal bacteria can spread through the air, by person-to-person contact, and it can be picked up from contaminated surfaces.

Once the bacteria reach the skin, they can go on to cause infection if they become heavily concentrated on the skin surface, or they are able to enter the body through a break in the skin. Staphylococcal bacteria often enter the body through an inflamed hair follicle or oil gland. Alternatively, they can enter through skin that is damaged by burns, cuts and scrapes, other infections, or insect bites.

Food poisoning

Staphylococcal food poisoning is usually caused by contamination of food with staphylococcal bacteria from a boil, or blister, on the skin of a food-handler.

If the food is not cooked thoroughly, or kept sufficiently hot, or cold, once the bacteria have come in contact with food they will continue to reproduce. As the bacteria reproduce, they produce a toxin that causes food poisoning when the affected food is eaten. Staphylococcal food poisoning is not spread from person-to-person.

Invasive staphylococcal infections

In healthy people, the layers of skin and the immune system usually provide a good defence that prevents a skin infection spreading further into the body.

Therefore, an opportunity for an invasive staphylococcal infection to occur will usually only arise if:

  • you have a weakened immune system due to an underlying medical condition, or due to a side effect of treatment,
  • you are using a piece of medical equipment that goes directly inside your body, and/or
  • you experience severe trauma to the skin, such as a deep impact wound, or a major burn.

Health conditions and treatments that can weaken the immune system include:

  • HIV,
  • diabetes (both type 1 and type 2),
  • chemotherapy,
  • alcohol abuse,
  • intravenous drug abuse (injecting illegal drugs, such as heroin), and
  • taking immunosuppressants (medication that suppresses the immune system and is used to help prevent the immune system from rejecting transplanted organs).

Medical equipment that can increase the risk of invasive staphylococcal infection include:

  • the equipment that is used to perform all types of dialysis (a medical procedure that involves placing either a needle into the vein, or a tube into the abdomen),
  • catheters (a catheter is a tube that is used to empty the bladder),
  • feeding tubes, and
  • breathing tubes.

Page last reviewed: 13/07/2011

Staphylococcal skin infections

A staphylococcal skin infection can usually be diagnosed by examining of the affected area of skin. A small piece of tissue may also be removed using a swab (a medical instrument that looks like a cotton bud) and tested for the presence of S. aureus bacteria.

Staphylococcal food poisoning

A diagnosis of staphylococcal food poisoning can be made by taking a sample of your stools (faeces) and testing it for the presence of bacteria.

Invasive staphylococcal infections

There are three main goals in diagnosing an invasive staphylococcal infection:

  • to confirm whether the infection has been caused by S. aureus bacteria and whether the strain of bacteria has developed a resistance to one or more antibiotics
  • to determine the source of the infection
  • to determine which other body functions have been affected and how badly

To do this, a number of tests may be carried out, including:

  • blood tests
  • urine tests
  • stool sample tests
  • blood pressure tests
  • a wound culture test, where a small sample of tissue, skin or fluid is taken from the affected area for testing
  • respiratory secretion testing, which involves testing a sample of saliva, phlegm or mucus
  • imaging studies, such as an X-Ray or CT scan
  • echocardiogram, where sound waves are used to scan the valves and chambers of the heart
  • kidney and liver function tests
  • a spinal tap, where a sample of cerebrospinal fluid is extracted from your back for testing (cerebrospinal fluid is the fluid that surrounds and protects the brain and spinal column)

Page last reviewed: 13/07/2011

Staphylococcal skin infections

Boils

In most cases, boils can be treated successfully at home. One of the best ways to speed up the healing process is to apply a warm facecloth to the boil for 10 minutes, three or four times a day.

The heat increases the amount of blood that circulates around the boil, resulting in more infection-fighting white blood cells being sent there.

Wash your hands thoroughly after touching the boil using soap and hot water as this will help prevent any bacteria being spread to other parts of your body or to other people.

Never attempt to squeeze or pierce the head of a boil because this can spread the infection.

Over-the-counter (OTC) painkillers, such as paracetamol or ibuprofen, can be used to relieve any pain caused by the boil.

Impetigo

Impetigo can usually be successfully treated using antibiotic cream (topical antibiotics).

Before applying the cream, wash any affected areas of skin using warm, soapy water. It is very important to wash your hands immediately afterwards. You could also use latex gloves when applying the cream.

Impetigo should respond to treatment within seven days. However, if the condition does not respond or the impetigo is widespread and severe, antibiotic tablets (oral antibiotics) will be prescribed.

A seven-day course of oral antibiotics is normally recommended. If you or your child are prescribed antibiotics, it is important to finish the course of medication even if symptoms clear up.

Cellulitis

Most cases of cellulitis are treated using antibiotics. Cellulitis usually responds quickly to antibiotics and you should soon find your symptoms starting to ease.

You may notice that your skin initially becomes redder when you first start taking the antibiotics, but this is normally only a temporary reaction. The redness should start to fade within 48 hours.

If your symptoms get worse 48 hours after taking the antibiotics, or you start to develop additional symptoms such as a high temperature or vomiting, contact your GP immediately.

Staphylococcal food poisoning

In most cases of staphylococcal food poisoning, you should be able to treat the symptoms at home without the need for medical attention.

If you have food poisoning, make sure you do not become dehydrated because this will make you feel worse and will slow your recovery time.

Dehydration is a risk because fluid is lost through vomiting and diarrhoea. Drink at least two litres (3.5 pints) of water a day, as well as 200ml (one-third of a pint) of water every time you pass a loose stool.

Invasive staphylococcal infections

Most cases of invasive staphylococcal infections need to be treated in hospital. This is because the functions of your body may need to be supported while the infection is treated.

Invasive infections are treated with injections of antibiotics (intravenous antibiotics). Most people will require a 7-10 day course of intravenous antibiotics.

If the strain of bacteria responsible for the infection is not resistant to antibiotics, an antibiotic called nafcillin is usually prescribed.

Side effects of nafcillin are naturally mild and include:

  • nausea
  • vomiting
  • abdominal pain

If the infection is caused by meticillin-resistant staphylococcus aureus (MRSA), an antibiotic called vancomycin is prescribed.

Side effects of vancomycin are uncommon, but they can be serious. They include:

  • allergic reactions, such as skin rashes, itching or hives and swelling of the face, lips or tongue
  • difficulty breathing
  • a change in amount or colour of your urine
  • a change in hearing, such as hearing loss
  • dizziness
  • redness, blistering, peeling or loosening of the skin, including inside the mouth
  • unusual bleeding, such as bleeding from the gums or nose
  • feeling unusually weak or tired

Page last reviewed: 13/07/2011

Staphylococcal skin infections

You can reduce your chances of developing a staphylococcal skin infection by washing your hands regularly, keeping your skin clean by having a bath or shower every day, and keeping any cuts clean and covered.

If you come into contact with someone with a staphylococcal skin infection, wash your hands thoroughly using warm water and soap if you touch the infected site or the pus that it produces.

If you have a staphylococcal skin infection, remove any pus that appears from the infected area immediately to prevent the infection from spreading from one part of your body to another. Clean the area with antiseptic or an antibacterial soap.

As S. aureus bacteria are easily transmitted from one person to another, towels, washcloths and bed linen that are used by someone with a staphylococcal infection should not be used by anyone else. They should be changed daily until the symptoms disappear and washed separately in hot water with bleach.

Staphylococcal food poisoning

The best way to prevent staphylococcal food poisoning is to ensure that food is both properly cooked and properly chilled.

Cooking food properly

Make sure that the food is cooked right through and is piping hot in the middle. With meat, insert a knife. If the juices that come out are clear and there is no pink or red meat left, the meat is fully cooked. Some meat, such as steaks and joints of beef or lamb, can be served rare (cooked for a short time to retain the juices of the meat) as long as the outside has been cooked properly.

If you reheat food, make sure that it is piping hot all the way through and never reheat food more than once.

Chilling food properly

It is important to keep certain foods at the correct temperature to prevent harmful bacteria from growing and multiplying. Always check the label on the packaging for the correct storage instructions.

Food that needs to be refrigerated should always be stored in the fridge. If food that needs to be chilled is left standing at room temperature, bacteria can grow and multiply to dangerous levels. Set your fridge temperature to 0-5C (32-41F).

Cooked leftovers should be cooled quickly, ideally within one to two hours, before being put in the fridge or freezer. Putting food in shallow containers and dividing it into smaller amounts will speed up the cooling process.

Invasive staphylococcal infections

If you have an increased risk of developing a staphylococcal infection because you have a weakened immune system, you will need to take extra precautions:

  • Do not smoke. Smoking will weaken your immune system.
  • Do not use illegal drugs. Illegal drugs will also weaken your immune system.
  • Eat a healthy diet. This will boost your immune system.
  • Take regular exercise. This will also boost your immune system.
  • Wash your hands regularly, particularly after going to the toilet, before and after preparing food, and after spending time in crowded places.

Content provided by NHS Choices www.nhs.uk and adapted for Ireland by the Health A-Z.

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