Staphylococcal infections


Staphylococcal infections


Staphylococcal infections are a group of infections caused by the bacterium Staphylococcus. You may have heard them referred to as staph infections.

The spectrum of staph infections can range from a minor boil or skin abscess to life-threatening infections such as septicaemia (infection of the blood) or endocarditis (infection of the lining of the heart).

There are many types of staphylococci, but most infections are caused by Staphylococcus aureus (S. aureus). S. aureus is common and often found in the nose or on the skin. Most of the time the bacteria do not cause any symptoms – this is referred to as colonisation.

Types of infection

Staph infections are caused when bacteria get into a break or cut in the skin. Depending how deep it goes, the type of infection can be broadly classified into two groups:

skin and soft tissue infections - such as impetigo or cellulitis

invasive infections - such as septicaemia (blood poisoning), septic arthritis (joint infection) or endocarditis (infection of the lining of the heart)

Skin infections are most common and usually cause symptoms such as boils or abscesses - painful, pus-filled lumps on the surface or just under the skin. This can lead to impetigo, which forms a crust on the skin, or cellulitis, which causes redness, swelling and pain in the skin and underlying tissue.  

In some cases an invasive infection can develop as a complication of a skin infection. The symptoms are more severe and wide-ranging and can include:

a high temperature (fever) of 38 degrees C (100.4 degrees F) or above

low blood pressure, which will cause you to feel dizzy when you stand up

confusion or disorientation

shortness of breath

Eating food contaminated with S. aureus bacteria will give you food poisoning. This normally develops after eating food, usually meat, that hasn't been cooked or stored properly.

Treating infections

Skin infections are usually mild and can be treated using antibiotic tablets or creams.

Invasive infections are more serious and usually treated in hospital with antibiotic injections.

Once the bacteria penetrate the skin and enter the blood or organs, they rapidly multiply and release toxins, which can cause other organs to stop working and a massive drop in blood pressure (toxic shock, a type of septic shock). These complications are life-threatening. 

How successful treatment is for people with invasive staph infections will depend on:

the person’s age

where the infection has spread to

whether the infection has caused complications

whether or not the person has any pre-existing health conditions, such as diabetes, a weakened immune system or heart disease

Preventing infection

The best way to prevent a staphylococcal infection is to regularly wash your hands and make sure any cuts and grazes are kept clean.

Who gets staph infections?

Staphylococcal skin infections are common, particularly among children, teenagers and young adults. Impetigo, for example, accounts for around 1 in 10 of all reported skin conditions in children.

Invasive staphylococcal infections are much less common. In England, it is estimated that about 1 in 3,300 people will develop an invasive infection in any given year.

You are more at risk of developing an invasive infection if you:

are having dialysis - used to treat people with advanced chronic kidney disease; the way dialysis is performed can sometimes allow bacteria to get inside the body

have a weakened immune system due to a condition, such as HIVor taking medication to suppress your immune system (immunosuppressants)

Antibiotic resistance

One of the biggest challenges in treating staphylococcal infections is that many strains of the bacteria have developed resistance against a number of different antibiotics.

Methicillin-resistant Staphylococcus aureus (MRSA) is a strain of the bacterium resistant to an old antibiotic called methicillin, which is no longer used, and flucloxacillin, an antibiotic commonly used for skin infection. 

Infections caused by MRSA can be severe and may need treatment by an injectable antibiotic.

As a result of concerns about increasing antibiotic resistance, there has been a shift in the way doctors prescribe antibiotics and they are now only prescribed when there is a clear need for them.

Symptoms of staphylococcal infections 

The symptoms of staphylococcal infections vary depending on the type of infection you have.

Staphylococcal skin infections

Staph infections most commonly affect the skin. Symptoms for the most common types of staphylococcal skin infections are outlined below.


A boil is a red, painful, lump on the skin that usually develops on the neck, face, armpit or buttocks. When a boil first forms, it appears as a swollen, painful red lump. As it grows, yellowish-white pus builds up at the centre of the boil.

As tempting as it may be, it is important not to squeeze a boil because it can lead to complications.

In most cases, the boil will eventually burst within a few weeks and the pus will drain away, leaving the skin to heal.

Skin abscess

An abscess is a painful collection of pus that may appear as a lump under the surface of the skin or an open break in the skin.

The abscess may get larger and more painful as the infection continues and more pus is produced.
Staphylococcal infections can cause skin abscesses on the head and neck, limbs, underarms and torso.


A hair follicle is a small sac in the skin that a hair grows out of. If a hair follicle becomes infected with staphylococcus bacteria then itchy, white bumps filled with pus can appear.

If the infection is deep in the skin, the infected hair follicle may develop into a boil (see above) and become more painful.


Impetigo is a highly contagious bacterial skin infection that mainly affects children. It does not affect the deeper skin layers. 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 (bullae)

The sores and blisters caused by both types of impetigo are usually very itchy. However, you should avoid scratching them because it can spread the infection to other parts of your body and the bacteria easily spread through close contact.


Cellulitis is a bacterial infection of the deep layer of the skin (dermis) and the layer of fat and soft tissues (the subcutaneous tissues) that lie underneath the skin. 

Cellulitis causes your skin to become:







Cellulitis can make you feel generally unwell and cause you to feel sick (nausea) or have shivers and chills.

 Wound infection 

Any wound has the potential to become infected, including cuts and grazes or surgical wounds.

Symptoms include:

redness, swelling and pain at the site of the wound

a discharge of pus or liquid from the wound

the wound healing much slower than would usually be expected

an unpleasant smell coming from the site of the wound

 Staphylococcal scalded skin syndrome 

Probably the most serious type of staphylococcal skin infection is staphylococcal scalded skin syndrome (SSSS), which most commonly affects babies and young children under five.

In this type of infection, the staphylococcal bacteria release a toxin (poison) that damages the skin, leading to extensive blistering which looks like the skin has been scalded by boiling water.

Other symptoms of SSSS include:

painful skin

a high temperature (fever) of 38C (100.4F) or above

large areas of skin peeling off or falling away

redness of the skin which usually spreads across the entire body

 Invasive staphylococcal infections 

Invasive staph infections are uncommon but potentially serious. Some of the types and their symptoms are described below.

 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

Septic bursitis

In septic bursitis, the bursa becomes infected. A bursa is a small fluid-filled sac which forms under the skin, usually over the joints and between tendons and bones.

Symptoms of septic bursitis include:

pain, swelling and tenderness in the affected body part which feels warm to the touch

a high temperature (fever) of 38C (100.4F) or above



Pyomyositis is an infection of the muscles used to move and support the bones of the skeleton. It is more common in tropical areas of the world.

Symptoms of pyomyositis include:

a very high temperature, which can be as high as 40C (104F)


pain and swelling in the affected muscles

the muscles feel soft and spongy to the touch due to the presence of pus


Osteomyelitis is a bone infection. One of the larger leg bones is usually affected.

Symptoms of osteomyelitis include:

a sudden high temperature

bone pain, which can often be severe

swelling, redness and warmth at the site of the infection

a general sense of feeling unwell

the affected body part is tender to touch

a restricted range of movement in the affected body part


Pneumonia is an infection of the lungs. Symptoms of pneumonia include:

difficulty breathing - your breathing may be rapid and shallow and you may feel breathless, even when you are resting

rapid heartbeat (tachycardia)

a high temperature (fever) of 38C (100.4F) or above

feeling generally unwell

pain in your chest

Toxic shock syndrome

Toxic shock syndrome is a rare condition caused when S. aureus bacteria enter the bloodstream and begin to release toxins (poisons). Most people are immune to the effects of the toxins, however in some people, the toxins can cause a drop in blood pressure and organ and tissue damage. The S. aureus can be found in a small wound, or associated with periods and using tampons.

Symptoms of toxic shock syndrome include:

a sudden high temperature


a skin rash that looks like sunburn


fainting or feeling faint

muscle aches



Endocarditis is an infection of the inner layer of the heart, particularly affecting the heart valves. The symptoms of endocarditis can sometimes develop gradually over many weeks or quickly over a few days.

Symptoms of endocarditis, caused by a staphylococcal infection, include:

a high temperature (fever) of 38C (100.4F) or above

chills and shivers

muscular aches and pains

chest pain


weakness and fatigue (extreme tiredness)


shortness of breath


Sepsis, also known as blood poisoning, can be due to any bacteria. The symptoms 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 causes you to feel dizzy when you stand up

a change in mental behaviour, such as confusion or disorientation


loss of consciousness

Sepsis is a medical emergency. Dial 999 to request an ambulance if you suspect that you or someone in your care is experiencing sepsis.

Staphylococcal food poisoning

The symptoms of staphylococcal food poisoning develop quickly after eating contaminated food (usually within 30 minutes to six hours). They include:

feeling sick (nausea)

being sick

stomach cramps


These symptoms should pass within one to three days. However, if your symptoms persist beyond this time, or if they worsen rapidly, you should contact your GP for advice.

Causes of staphylococcal infections 

There are many types of staphylococcus bacteria, but most infections are caused by Staphylococcus aureus (S. aureus).

S. aureus is common in humans. It's 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.

In England, it is estimated that 4 out of 5 people will be colonised by S. aureus at least once in their life, and that 1 out of 5 people are persistently colonised.

Skin infections

Staphylococcal (staph) bacteria can spread through the air, by person-to-person contact and they can also 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 surface of the skin or if they enter the body through a break in the skin.

Staph bacteria often enter the body through an inflamed hair follicle or oil gland. They can also enter through skin damaged by burns, cuts and scrapes, other infections or insect bites.

PVL-producing Staphylococcus aureus

A minority of S. aureus bacteria can produce a substance called Panton-Valentine leukocidin (PVL), which kills the white cells, causing the body to make more white cells to continue to fight the infection.

PVL-producing strains of bacteria are therefore more likely to cause repeated skin infections, such as boils and abscesses. They can also cause more serious conditions such as:

sepsis – blood poisoning caused by bacteria multiplying in the blood

pneumonia – swelling (inflammation) of the lungs caused by an infection

Invasive staphylococcal infections

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

An invasive staph infection usually only develops if you:

have a weakened immune system due to an underlying medical condition or due to a side effect of treatment

use medical equipment that goes directly inside your body, and/or

experience severe trauma to the skin, such as a deep wound or a major burn

Medical equipment that increases your risk of developing invasive staphylococcal infections include:

equipment used to perform all types of dialysis

urinary catheters (a tube used to empty the bladder)

feeding tubes

breathing tubes

 Food poisoning 

Staphylococcal food poisoning is usually caused by food contaminated with staphylococcal bacteria from the skin of someone who handles food.

If the food is not cooked thoroughly, or if it's not kept hot or cold, the bacteria will continue to reproduce when they come in contact with it. The bacteria then produce the toxin (poison) that causes food poisoning.

It is not possible for staph food poisoning to be spread from person-to-person.


Diagnosing staphylococcal infections 

Staphylococcal infections are diagnosed in different ways depending on your symptoms and the type of infection you have.

Staphylococcal skin infections

A staphylococcal skin infection is often diagnosed by examining the affected area of skin. A small piece of tissue may also be removed using a swab and tested for Staphylococcus aureus (S. aureus) 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 bacteria have developed resistance to one or more antibiotics

to determine the source of the infection

to determine which other functions of the body 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 computerised tomography (CT) scan, or an echocardiogram - where sound waves are used to scan the valves and chambers of the heart

kidney and liver function tests

a lumbar puncture - where a sample of cerebrospinal fluid is removed from your back for testing

Staphylococcal food poisoning

Staphylococcal food poisoning can be diagnosed by taking a sample of your stools (faeces) and testing it for bacteria. However, in most food poisoning cases there is usually no need to carry out a diagnosis as it passes within a few days.

You only need to see your GP if:

your symptoms are severe and not getting better

you have symptoms of severe dehydration, such as sunken eyes and are unable to urinate

there has been an outbreak of similar cases of food poisoning linked to a possible source of contamination

Treating staphylococcal infections 

Most staphylococcal infections are treated with antibiotics or bydraining the infection. Invasive staphylococcal infections will often require hospital treatment.

Staphylococcal skin infections

Once your doctor has diagnosed which type of infection you have, they will usually prescribe a course of antibiotics. It's important to finish the course of medication even if the symptoms clear up.

Antibiotics can be used to treat the following staphylococcal infections.

Folliculitis - Antibiotic cream or tablets may be prescribed to treat folliculitis. Your doctor may also recommend that you avoid shaving the affected area until the infection clears.

 Antibiotic cream can usually be used to treat impetigo. A seven day course of tablets may be prescribed if the condition does not respond, or if the impetigo is widespread and severe. 

Cellulitis usually responds quickly to antibiotics and you should soon find your symptoms starting to ease. 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. .

Wound infection - Depending on the severity and the extent of your infection, antibiotic tablets or injections may be recommended. In the most severe cases, surgery may be needed to remove dead or damaged tissue from the wound.

Staphylococcal scalded skin syndrome (SSSS) - SSSS and toxic shock are usually regarded as a medical emergency because the infection can spread beyond the skin and into the body. It requires prompt treatment with antibiotic injections.

Boils and abscesses

Smaller boils and abscesses can often be treated at home. You can wait for them to drain naturally and then cover the wound with a sterile gauze or dressing or apply a warm facecloth to the boil for 10 minutes, three or four times a day, to speed up the healing process. Wash your hands thoroughly after touching a boil to prevent the bacteria spreading.

Your GP will probably need to treat larger boils and abscesses, particularly if they are soft and spongy - as this means they are unlikely to burst by themselves. Your GP will remove the pus using a technique called incision and drainage. In some cases, your GP may refer you to your local hospital to have this procedure.

Incision and drainage involves piercing the tip of the boil or abscess with a sterile needle or scalpel. This encourages the pus to drain out which should help relieve pain and stimulate the healing process. Before having the procedure, you are likely to be given local anaesthetic to numb the affected area.

As tempting as it may be, you should never attempt to squeeze or pierce the abscess or boil yourself because this can spread the infection.

If you have had a lot of boils and abscesses, it may be because of underlying diabetes or because you are carrying an uncommon type of bacteria called PVL-producing S. aureus.

Invasive staphylococcal infections

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

Invasive infections are treated with antibiotic injections. Most people will require a seven to 10 day course.

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 usually mild and include nausea, vomiting and 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 if they occur 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 the amount or colour of your urine

a change in hearing, such as hearing loss


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

Staphylococcal food poisoning

Most cases of staphylococcal food poisoning can be treated at home without the need of medical attention. It's important to make sure you do not become dehydrated because this will slow your recovery time.

Fluid can be lost through vomiting and diarrhoea so try to sip water regularly throughout the day, particularly after passing a loose stool.