Diphtheria

Diphtheria is a contagious bacterial infection that mainly attacks the throat and nose and sometimes the skin. Where nearly all children are immunised, a doctor may finish a whole career without seeing a single case. But the disease has not gone away: it returns whenever vaccination coverage slips, and the last large European outbreak happened not in some distant century but within living memory. What makes it dangerous is not the bacterium itself but the poison it manufactures, which travels in the blood and reaches the heart and the nerves. That is why this illness is counted in hours rather than days.

What this bacterium does

The organism responsible is the diphtheria bacillus. Some of its strains produce a toxin and some do not, and that is what decides whether the illness is severe or mild.

Wherever the bacterium settles, the toxin kills cells, and out of dead tissue, blood and microbes a membrane forms: dense, greyish white, welded to the lining underneath. That is the feature which separates diphtheria from ordinary tonsillitis, where the coating lifts away easily. The diphtheritic membrane does not lift, and the surface bleeds if you try to scrape it off. On no account should anyone attempt to remove it.

The toxin is then absorbed into the blood and carried around the body. The heart muscle, the nerves and the kidneys take the worst of it, and it is that damage, not the sore throat, which decides the outcome. The longer the toxin works without an antidote, the greater the share of it that manages to bind irreversibly to cells.

The same illness is also caused by a related bacterium, Corynebacterium ulcerans. That one is not caught from people but from animals, from cattle, goats, cats and dogs, and through unpasteurised milk. Such cases are rare and hardly ever thought of. The vaccine protects against this variant as well.

How it spreads

The main route is the air: coughing, sneezing, talking, close company. It also passes through shared cups, cutlery, towels and bedding, since the bacterium survives for a while on objects. The skin form spreads by direct contact with the sores and, in crowded conditions, travels even more readily than the throat form.

One feature makes the infection particularly hard to stop: a person can carry the bacterium in the throat without falling ill and still infect everyone around them. Carriers are more often the vaccinated, because the vaccine protects them from the toxin but does not stop the bacterium taking up residence in the throat. That is why, once a case is found, the whole circle of contacts is tested and not only those who feel unwell.

Between catching it and the first signs there are usually two to five days, occasionally up to ten.

How the illness begins

The opening is deceptively quiet. The temperature is often moderate and the throat hurts bearably, yet the person weakens far more than that temperature would explain. That mismatch is a significant clue.

Then the rest arrives:

• a greyish white membrane on the tonsils spreading onto the soft palate and the uvula, and sometimes into the nose or downward into the voice box;
• enlarged, tender glands in the neck; in severe cases the neck swells until it loses its outline;
• difficulty swallowing, a lump in the throat, a sickly sweet smell on the breath;
• hoarseness, a barking cough and noisy breathing, which mean the voice box is involved and is the quickest route to real trouble, particularly in small children;
• in the nasal form, blood-stained or purulent discharge from one nostril and crusting under the nose, which in toddlers looks like a cold that never ends.

Skin diphtheria looks quite different: an ulcer that will not close, with sharp edges and a dirty grey base, usually on the legs, feet or hands and on the site of a small wound, bite or rub. It may barely hurt and can drag on for months. Severe complications in this form are uncommon, but the person is every bit as infectious as anyone else.

Complications and the signs that mean an ambulance

Three things make diphtheria lethal. The first is the membrane blocking the airway. The second is inflammation of the heart muscle, which creeps up in the second or third week, once the throat has cleared and the person believes they have recovered; it causes rhythm disturbances and a weakened heart and is the commonest cause of death. The third is nerve damage: the soft palate goes first, so the voice turns nasal and liquids come back through the nose, then close-up vision blurs, then the arms and legs weaken and, in severe cases, the breathing muscles. Nerves recover slowly but as a rule completely.

Call an ambulance at once if any of the following appears:

• breathing is difficult, noisy or wheezy, the spaces between the ribs and the hollow above the breastbone are pulled in, or the person sits up and braces their arms in order to draw breath;
• they cannot swallow even saliva and it runs from the mouth;
• the neck has visibly swollen;
• lips or face have turned blue, the skin is pale, cold and clammy;
• fainting, a pulse that has slowed abruptly or gone fast and irregular, chest pain, breathlessness when lying flat;
• liquids escaping through the nose, choking on drinks, double or blurred vision, and weakness in the limbs that is getting worse.

Say straight away that diphtheria is suspected: both the crew and the hospital need warning in advance. Across most of Europe the single emergency number 112 will reach an ambulance.

How it is treated

Treatment happens in hospital and in isolation. The two mainstays do quite different jobs.

The first is diphtheria antitoxin, the antidote proper. It binds the toxin still circulating in the blood but can do nothing about the portion already fixed to the cells of the heart and nerves. Hence the central rule: it is given on the clinical picture, without waiting for the culture result, because every day lost raises the risk of complications. It is made from horse serum, so tolerance is checked beforehand and it is given where an allergic reaction can be dealt with.

The second is antibiotics, usually a penicillin or a macrolide, over a course of about two weeks. They kill the bacterium and end the infectiousness, but they do not neutralise toxin that has already been made, so they cannot stand in for the antitoxin.

Added to that are rest and close watching of the heart: tracings are repeated even once the person feels well, and exertion is restricted for weeks precisely because of that late heart inflammation. If the airway threatens to close, a tube is placed or an opening is made in the neck. Skin ulcers are cleaned and dressed; they heal over two or three months and often leave a scar.

And the point most often forgotten: having had diphtheria does not leave reliable protection behind. It is possible to catch it again, so after recovery the person is vaccinated afresh with a full course. Clearance swabs are taken before going back to school or work.

The vaccine: what it gives and how long it lasts

This vaccine is built in an unusual way: it teaches the body to neutralise the toxin rather than the bacterium. Hence two sides of one coin. The good side is that a vaccinated person is at almost no risk of dying from diphtheria even if they catch it. The sobering side is that the bacterium can still settle in their throat and they can pass it to an unvaccinated child.

The first doses are given in the first year of life, followed by boosters in the preschool years and in adolescence. The exact timing belongs to each country, so follow your own national immunisation schedule rather than somebody else's.

Adults need to top the protection up roughly every ten years, usually with a combined vaccine that also covers tetanus. Most adults were last vaccinated at school and do not remember it, which means their protection faded long ago. It is worth checking the date:

• before travelling to a country with low vaccination coverage or an outbreak under way;
• with any wound you see a doctor about, alongside the tetanus question;
• when planning a pregnancy: in many countries the combined vaccine is also given during pregnancy, chiefly to protect the newborn against whooping cough, and it refreshes diphtheria protection at the same time;
• if you work with people from regions where diphtheria still occurs.

It is generally well tolerated: soreness and swelling at the injection site and sometimes a mild temperature for a day or two.

If someone close to you falls ill

Everyone in close contact with the patient, household members, a partner, anyone who drank from the same cup, needs three things: a throat and nose swab, about a week of watching themselves, and a preventive course of antibiotic. Plus a vaccine dose if the last one was many years ago; the doctor sets the exact interval. All of it is arranged even when the person feels perfectly well, and that is precisely the reason for it, since carriage produces no symptoms.

The antibiotic is chosen by the doctor and comes together with follow-up swabs: if a result is positive, the course continues until the bacterium stops growing. In the meantime it is worth giving each person their own crockery and towels at home, washing linen hot and airing the rooms; ordinary household cleaning products are enough.

Online consultation

A remote appointment suits everything that is done in advance and without haste. The doctor can go through your immunisation record and say whether a booster is needed before a trip and how far ahead to have it; work out what to do if a case has turned up among your contacts; and help make sense of a sore throat that is dragging on when there is neither a membrane nor any contact with a patient. It is also worth coming after discharge, with the question of when to return to physical activity and which heart checks are still to come. What cannot be judged through a screen is a membrane in the throat, a swollen neck or any difficulty breathing: those go straight to emergency care.

This material is for information only and does not replace medical advice.