What is diphtheria?
Diphtheria is an acute infectious disease caused by a bacterium called Corynebacterium diphtheriae. This disease affects the upper respiratory tract and very occasionally the skin. Virulent strains of C. diphtheriae produce a toxin which can damage heart and nervous tissues, although non-toxigenic strains can cause a localised infection. A diphtheria-like illness is sometimes caused by another toxin-producing bacterium Corynebacterium ulcerans. Immunisation against diphtheria was introduced on a national scale throughout the United Kingdom in the early 1940s and resulted in a dramatic drop in the number of cases and deaths from the disease. For example, in 1940, 46,281 cases and 2,480 deaths were notified, compared with 37 cases and six deaths in 1957. Diphtheria is now rare in England and Wales, nearly all new cases are acquired abroad, and only two deaths due to diphtheria have been recorded since 1972.
How does diphtheria spread and what symptoms does it cause?
Humans are the only known source of C. diphtheriae and the disease is spread by infected droplets or secretions from the nose and throat of a recent case or someone who, without any symptoms, is carrying the bacterium in their nose or throat. After an incubation period of usually between two and five days a new case may become generally unwell with a mild fever, headache, rapid pulse and sore throat. Swelling of the throat tissues may occur leading to breathing difficulties. The swelling is due to inflammation of the lining of the throat resulting in an exudate or 'membrane' which is typically pale grey or white in colour and firmly stuck to the throat. Sometimes the infection is confined to the nose causing a foul smelling, bloodstained discharge. Progression of the illness then depends on whether or not the infecting strain of C. diphtheriae produces toxin and the amount of immunity already possessed by the patient from previous diphtheria immunisation. Milder cases will usually have an uneventful recovery once the throat membrane disappears after about a week. More serious infections are characterised by increasingly severe heart and nervous system complications which develop after two to six weeks and can lead to collapse, paralysis, coma and death. About 5 to 10% of diphtheria cases die.
Chronic skin lesions due to diphtheria are unusual and occur particularly in the tropics. The lesions may be due to either toxigenic or non-toxigenic strains of C. diphtheriae. Spread of this infection is by direct contact with the infected lesions. The diagnosis and treatment of cases and the management of contacts is similar to diphtheria of the respiratory tract.
How is diphtheria diagnosed?
Swabs are taken from the nose and throat of the patient suspected of having diphtheria, ideally before antibiotic treatment is started. Any wounds or skin lesions are also swabbed. These swabs are sent to a Microbiology laboratory where the bacterium can be grown on special culture media. If C. diphtheriae is isolated then the bacterium will be tested to see whether or not it produces toxin as this will determine how the patient's illness is likely to progress and how much at risk are the patient's close contacts. In addition to swabs, a blood sample should also be collected from the patient before any antitoxin treatment is given, to measure their antibodies to diphtheria toxin; a second 'convalescent' blood sample should be collected about two weeks later to re-measure these antibodies.
How are diphtheria cases treated?
Patients with diphtheria require urgent admission to hospital where they will be nursed in isolation. If diphtheria is confirmed then they will remain isolated until their treatment has been completed and negative cultures have been obtained from repeat nose and throat swabs. Treatment consists of an injection of antitoxin to counteract the effects of the toxin produced by C. diphtheriae and antibiotics, such as penicillin or erythromycin by injection and then by mouth for a total of seven to fourteen days, to kill the bacteria. Antitoxin and antibiotics are usually commenced before there is bacteriological confirmation of the infection. If necessary, action is taken to assist the patient's breathing and bedrest, together with general nursing and medical care, is given as required. Finally, clinical diphtheria does not confer any immunity and therefore the patient should receive diphtheria immunisation either as a primary course or as a booster dose of vaccine before discharge from hospital.
How are further cases prevented in those who are in close contact with a case of diphtheria?
Once diphtheria due to a toxigenic strain is either strongly suspected or confirmed, then a number of public health measures are urgently undertaken. Anyone who has had close contact with the case in the previous seven days, such as other household members, regular visitors to the patient's house, kissing or sexual contacts of the case should be assessed for signs and symptoms of diphtheria on a daily basis for seven days. They should also have nose and throat swabs taken to see whether they have become carriers. This is likely to have happened in up to a quarter of close contacts. However, contacts in either a school classroom, workplace or hospital are at much lower risk.
All close contacts, whether or not they have received diphtheria immunisation in the past and irrespective of their nose and throat culture results, should be given a suitable antibiotic either as a single dose by injection or as a seven-to-ten day course by mouth. Those close contacts found to be carriers will require a second throat swab after completing their antibiotics, to ensure they are now clear of carriage. A further ten-day course of antibiotics may be needed if carriage has not been completely eradicated. In addition, all contacts who have previously received diphtheria immunisation should be given a booster dose of vaccine unless their last dose of vaccine was within the previous 12 months. All unimmunised contacts should be given a full course of three injections of diphtheria vaccine. Contacts of cases due to non-toxigenic strains are not at risk and no further action is necessary.
What are the recommendations for immunisation against diphtheria?
Diphtheria immunisation has been available in the United Kingdom for over 50 years. It is recommended for all infants from two months old. The primary course of immunisation consists of three doses starting at two months with an interval of one month between each dose. In these circumstances the diphtheria vaccine is normally part of a triple vaccine of diphtheria, tetanus and pertussis, although the pertussis part of the vaccine may be omitted. A booster dose of vaccine containing both diphtheria and tetanus is also recommended for children immediately before school entry and again for school-leavers aged between fifteen and nineteen. A special low-dose diphtheria vaccine is available for the primary immunisation of children aged 10 or more years and all adults. This low dose vaccine is also used to give booster doses of vaccine, e.g. to those in close contact with a case of diphtheria, for all persons aged 10 years and over.
Diphtheria in the former Soviet Union
An epidemic of diphtheria in the Russian Federation and the Ukraine began in 1990 and has now spread to the neighbouring newly independent states. During 1994, 47,853 cases were reported from these countries, representing 87% of diphtheria cases within the World Health Organisation European region. The World Health Organisation predicts a total of 60,000 new cases for 1995. All age groups are affected, but the highest number of cases are in children aged seven to fourteen years. Unvaccinated travellers to any of the fifteen countries in the newly independent states should receive a full course of diphtheria vaccine before departure; a booster dose of vaccine is recommended for those going to live or work with the local people if their last dose of vaccine was given more than 10 years ago.