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Infectious Diseases

Updated 03 June 2015

Diphtheria

This is an infectious bacterial disease affecting the respiratory tract, and sometimes skin.

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Summary

  • Diphtheria is a highly infectious bacterial disease that usually affects the respiratory tract, and sometimes the skin.
  • Complications include breathing problems and organ damage, which may be fatal.
  • A characteristic symptom is a thick coating or "false membrane" in the nose or throat.
  • There is an effective vaccine to prevent diphtheria; most cases occur among unvaccinated or inadequately vaccinated people.
  • Treatment involves administration of diphtheria anti-toxin and antibiotics.

Description
 

Diphtheria is an acute, highly infectious bacterial disease that usually affects the respiratory tract (mainly the nose, throat, voice-box and tonsils), and sometimes the skin. Diphtheria that affects the respiratory tract is referred to as respiratory diphtheria; that which affects the skin is called cutaneous diphtheria.

Complications of diphtheria include breathing problems and organ damage, which may be fatal.

Cause

Diphtheria is caused by the bacterium Corynebacterium diphtheriae. The bacteria produce a toxin that causes tissue damage in the immediate area of the infection, primarily the nose and throat. The toxin can spread via the bloodstream to other organs where it can cause significant damage. The tissue of the heart and nerves are those most frequently and severely affected.

Diphtheria is highly contagious: it is easily transmitted to others through close contact with discharge from an infected person's nose, throat, eyes and/or skin lesions. Transmission is usually by respiratory droplets i.e. by breathing in the bacteria after an infected person has coughed, sneezed or laughed. It can also be transmitted by contaminated objects (such as drinking from a glass used by an infected person) or foods (such as contaminated milk).

People carrying diphtheria germs are contagious for up to four weeks, even if they themselves develop no symptoms.

Who gets it and who is at risk?

Most cases of diphtheria occur among unvaccinated or inadequately vaccinated people. Diphtheria is rare in developed countries, but is still common in developing countries where children are not routinely immunised. It also poses a threat to travellers – people with declining immunity to diphtheria, e.g. older people who were vaccinated many years ago may be exposed to diphtheria in countries where it is still common and may get infected. A major outbreak occurred in the countries of the former Soviet Union in the early 1990s because of a breakdown in their immunization programmes.

Children under five years old and adults over 60 are particularly at risk for contracting diphtheria, as are people living in crowded or unhygienic conditions, or who are undernourished.

Cutaneous diphtheria is typically a slow-developing, chronic infection, seen most often in the tropics. It may also occur in contexts of poverty and poor hygiene.

Symptoms and signs

Symptoms usually appear two to four days after infection, with a range of one to six days. The disease may sometimes be so mild that it is not recognised. There may be no symptoms.

Initially diphtheria causes local symptoms, the nature of which depend on the site of infection. Thus most commonly the throat is infected causing a sore throat. If the nose is infected there may be a bloody watery discharge from the nose and if the voice box or larynx is infected the person may be hoarse or have a barking kind of cough. These symptoms are not specific for diphtheria and are these days far more likely to be caused by other bacterial or viral infections.

Most people with diphtheria also have a low-grade fever and chills. The (lymph) glands in the neck are usually swollen. These symptoms can occur in many other infections. Sometimes the swelling of the glands is very severe causing the so-called ‘bull neck’ appearance. This is suggestive of diphtheria.

Over the following few days the diphtheria toxin causes local tissue damage at the infected sites. The tissues appear to be coated with a grey-brown membrane, called a false membrane. The false membrane cannot be removed without causing bleeding from underlying tissue. This false membrane is a characteristic feature of diphtheria, i.e. it isn’t seen in other kinds of infections. However, it is also only present in about half of people with diphtheria and indicates more severe disease.

The false membrane can get quite big and can cause a blockage in the windpipe. This leads to stridor (harsh, high pitched sound during breathing, sometimes called croup), difficulties with breathing and if severe, lack of oxygen in the body (seen as a blue colour to tongue). The false membrane can also cause difficulty in swallowing. Children have smaller airways and are therefore more at risk of obstruction (blockages). These symptoms can be caused by a number of other infections. However, they always indicate a severe problem and medical attention must be sought urgently.

Usually the effects of the toxin on the heart and nerves do not show until about one to two weeks after the start of the illness. However, sometimes the nerves to the roof of the mouth (the palate) can be affected early on, leading to regurgitation of swallowed liquids through the nose. If the nerves are affected, there may be weakness of muscles controlling the eyes and facial movements as well as the legs and arms. If the heart is affected there may be signs of heart failure, e.g. shortness of breath, rapid irregular heartbeat.

Diagnosis

A physical examination may reveal characteristic signs of diphtheria such as the grey membrane in the throat, enlarged lymph glands, and swelling of the neck or larynx. If diphtheria is suspected, treatment should be started immediately, without waiting for laboratory test results.

To confirm the diagnosis, a smear is taken of an infected area. This is then tested in the laboratory to identify Corynebacterium diphtheriae.

Treatment

Immediate treatment and hospitalisation should follow a diagnosis of respiratory diphtheria.

Treatment involves administration of diphtheria anti-toxin to neutralise the toxin circulating in the body, as well as antibiotics (such as penicillin or erythromycin) to kill the remaining bacteria. The anti-toxin is given as an intramuscular or intravenous injection. You are closely observed while the anti-toxins are given in case the solution causes an allergic reaction. Your heart will be monitored due to the possibility of myocarditis (inflammation of the heart muscle). Antibiotic treatment usually renders you non-infectious within 24 hours.

If the infection is advanced, and airway obstruction is present, you may need mechanical assistance to breathe. This will involve insertion of an endotracheal tube (into the windpipe) and/or removal of the obstructing membrane.

Where the toxin has spread to the heart, kidneys or central nervous system, you may need intravenous fluids, oxygen or cardiac medications.

Family members who have not been immunised, or who are very young or elderly, must be protected from contact with the infected person. Your doctor will treat anyone who may have been exposed to the bacteria: this will include assessment of their immune status, throat cultures, booster doses of diphtheria vaccine, and prophylactic antibiotics for those contacts who may not have immunity.

Skin infections are treated with antibiotics, although some longstanding cases may not require anti-toxin.

Bed-rest is recommended in the acute phase and may need to be prolonged especially if the heart has been affected. It is wise to resume normal activities gradually.

Once you have recovered, you should still receive a full course of diphtheria vaccine to prevent a recurrence. Contracting the disease does not guarantee immunity.

Prevention

Preventing diphtheria depends almost entirely on immunisation. The diphtheria vaccine is very safe and effective. Children receive a combined vaccine called DTP or DTaP (diphtheria-tetanus-pertussis). The DTP vaccine is routinely given at six, ten and 14 weeks of age, with booster doses at 18 months and at four to six years. Booster DT shots should be given every 10 years after that to maintain immunity.

For non-immunised adults, a combination shot, called a DT or Td booster, protects against tetanus and diphtheria. DT vaccine is recommended for all adults who have not been immunised within the past 10 years.

Recovery from diphtheria is not always followed by lasting immunity, so even people who have had the disease need to be immunised.

Travelling to high-risk areas

If travelling to high-risk areas, an accelerated immunisation schedule is recommended for children who have not completed their immunisations. Unvaccinated persons over seven years old should receive three doses of DT vaccine. The first two doses should be separated by four to eight weeks, and the third dose given six to twelve months after the second.

Side-effects

Although most children tolerate it well, the DTP vaccine sometimes causes mild side-effects such as redness, tenderness or swelling at the injection site; low fever; or fretfulness. Severe complications, such as an allergic reaction or seizure, are rare.

Side-effects from the DT vaccine are very rare. When these do occur, they usually comprise soreness, redness or swelling at the injection site, and slight fever.

The potential risks associated with diphtheria are much greater than those associated with being vaccinated.

Outcome

Immediate hospitalisation and early intervention allows most people to recover from diphtheria. However, even with proper treatment, between 5% and 10% of diphtheria patients die. The death rate for untreated cases is 40-50%.

Complications of diphtheria

Complications of respiratory diphtheria include:

  • Breathing problems due to airway obstruction
  • Diphtheria toxin can spread via the bloodstream and damage organs such as the heart, nervous system or kidneys. This can result in potentially life-threatening complications, including:
    • Myocarditis, which can lead to heart failure.
    • Nerve damage, such as peripheral neuritis (inflammation of the peripheral nerves) causing unco-ordinated movements and other symptoms. Severe nerve damage can cause paralysis. Usually the nerves recover fully, but this can take a long time (weeks to months).

When to call the doctor

Call your doctor immediately if you or anyone you know shows symptoms of diphtheria, or is exposed to the disease.

If you're not sure if your child has been vaccinated against diphtheria, consult your doctor. Ensure that your own booster immunisations are current.

Reviewed by Dr Andrew Whitelaw, MBBCh (Witwatersrand), MSc (UCT), FCPath (Micro) (SA) Senior registrar, Department of Microbiology, University of Cape Town and Groote Schuur Hospital

 

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