The Nigerian government recently confirmed a diphtheria outbreak in parts of the country. The disease is a highly contagious infection caused by a bacterium called Corynebacterium species that affects an individual’s nose, throat, and, in some cases, skin.
What is diphtheria?
Diphtheria is a severe bacterial disease caused by the spread of a bacterium, Corynebacterium species, mainly by toxin-producing Corynebacterium diphtheriae and rarely by toxin-producing strains of C. ulcerans and C. pseudotuberculosis, NCDC explains.
When a person catches diphtheria, the bacteria release toxins or poison into the person’s body. America’s Centre for Disease Control and Prevention (CDC) said the toxin infects the upper airways and sometimes the skin, causing a membrane to grow across the windpipe.
“This makes breathing hard, and if the membrane completely blocks the windpipe, it can lead to suffocation and death. The heart and nervous system can also be damaged,” CDC noted.
Diphtheria manifests as laryngitis, pharyngitis or tonsillitis and is associated with an adherent membrane covering the tonsils, pharynx and/or nose.
Beyond the respiratory symptoms, NCDC said, approximately a quarter of cases may develop heart problems (myocarditis). The mainstay of Diphtheria treatment is antibiotics and Diphtheria antitoxin (DAT).
Transmission
Diphtheria spreads easily among people by direct contact or through the air and through respiratory droplets from coughing or sneezing, NCDC added.
“It may also be spread by contaminated clothing and objects. A person is infectious for as long as the bacteria are present in respiratory secretions, usually two weeks without treatment and seldom more than six weeks.
“In rare cases, chronic carriers may shed organisms for six months or more. Effective treatment promptly terminates shedding in about one or two days,” NCDC said.
According to the CDC, diphtheria can be transmitted by sharing items such as cups, cutlery, clothing or bedding with an infected person. It is possible to get diphtheria more than once.
Who’s at risk of developing diphtheria?
Anyone who is not protected by the vaccine and comes in close contact with an infected person can develop diphtheria, according to Cleveland Clinic, an American non-profit academic medical centre.
Symptoms
The most common type of diphtheria is classic respiratory diphtheria. An infected person typically shows signs of diphtheria around two to five days after exposure.
The length of time for symptoms to show can be anywhere from one to 10 days after exposure, said Tijjani Yakubu, a medical doctor at the Federal Medical Centre, Abuja. “Initial symptoms may be mild and include fever, runny nose, sore throat, cough, and red eyes (conjunctivitis).”
In some cases, Mr Yakubu said, infected persons “experience swollen neck glands, problems breathing due to tissues obstructing the nose, throat, kidney, or heart problems (if the bacteria enters the bloodstream).”
In severe cases, NCDC states that the bacteria produce an exotoxin that causes a thick grey or white patch (pseudo-membrane) on the tonsils and/or at the back of the throat.
“This can block the airway making it hard to breathe or swallow and causing a barking cough. The neck may swell partially due to enlarged lymph nodes and frequently confer a bull-neck appearance.
“The exotoxin produced by the bacteria may also enter the bloodstream causing complications such as inflammation and damage of the heart muscle, inflammation of nerves, kidney problems, and bleeding problems due to decreased blood platelet count.
“The damaged heart muscles may result in an abnormal heart rate, and inflammation of the nerves may result in paralysis. The infection can also affect the skin (cutaneous diphtheria). More rarely, it can affect mucous membranes at other non-respiratory sites, such as the genitalia and conjunctiva,” NCDC stated.
Causes
Mr Yakubu said diphtheria is a serious infection caused by strains of bacteria called Corynebacterium diphtheriae that make a toxin.
“It is the toxin that can cause people to get very sick,” Mr Yakubu said.
On their part, Cleveland Clinic researchers said diphtheria is caused by bacteria adhering to the lining of respiratory system.
“These bacteria generate a toxin that damages your respiratory tissue cells. The tissue left behind within two or three days forms a bulky, grey coating. This coating has the potential to cover tissues in your voice box, throat, nose and tonsils. For the infected person, breathing and swallowing become hard to do.”
Complications
NCDC said complications due to diphtheria usually occur in the second and third week following infection.
“This includes corneal scarring (aggravated by vitamin A deficiency), encephalitis (more common in older children and adults, 0.1 per cent), diarrhoea, pneumonia (a major cause of death) and subacute sclerosing panencephalitis (rare, delayed complication; associated personality changes, seizures, motor disability, progressing to coma and death).
According to NCDC, “Case fatality ratios up to 10 per cent have been reported in diphtheria outbreaks and are higher in settings where diphtheria antitoxin (DAT) is unavailable.”
Types of diphtheria
According to the CDC, there are two main types of diphtheria – classical respiratory and cutaneous.
Classical respiratory diphtheria is the most common type of diphtheria. It may affect the nose, throat, tonsils or larynx (voice box). “Symptoms can vary depending on where the affected membranes are located in the body. Some people call this condition pharyngeal diphtheria (diphtheria of the throat),” CDC added.
Cutaneous diphtheria is described as “the rarest type of diphtheria, characterised by skin rash, sores or blisters, which can appear anywhere on your body. Cutaneous diphtheria is more common in tropical climates or crowded places where people live in unhealthy conditions.”
Diagnosis
According to Mr Yakubu, the Abuja-based doctor, healthcare providers will diagnose based on symptoms and a lab test.
“They will use a swab to take a sample from the back of your throat or a sore,” the medical doctor said, noting that the swab would be taken to a lab for diagnosis.
NCDC also explains diphtheria testing broadly, saying clinical diagnosis of diphtheria usually relies on a greyish/whitish membrane (pseudo-membrane) covering the throat (pharynx/tonsils).
Although laboratory investigation of suspected cases is recommended for case confirmation, treatment should be started immediately before laboratory results are received, the centre added.
“Two samples should be collected from every suspected case at first contact with the case – a pharyngeal swab and a nasal swab – and should ideally be taken before starting antibiotics. However, samples should still be taken even if antibiotics have already been started. Specimens should be placed in an appropriate transport medium (Amies transport medium or Stuart medium) or silica gel sachets in the case of a dry swab. Transport these to the laboratory promptly at 2–8oC,” NCDC said.
“If possible, a sample of the pseudo-membrane should also be collected and placed in saline (not formalin). A culture collected from a wound should be handled the same as nasal and throat swabs,” the centre explained. “The most reliable method of confirming diphtheria is by the culture of the organism from any of the specimens mentioned above and by demonstrating toxin production using an immunoprecipitation reaction (the modified Elek test.)”
“PCR can be done directly on swab material to detect the presence of the A and B subunits of the diphtheria toxin gene (tox). However, in some cases, the presence of tox does not confirm the production of toxin; positive PCR results should therefore always be confirmed with the Elek test if there is an isolate,” NCDC said.
Treatment
Diphtheria infection is treated with a diphtheria antitoxin (DAT) administered intravenously or through an intramuscular injection. The Nigerian disease control agency said that antibiotics could also be given to eliminate the bacteria to prevent transmission and toxin production to others.
“Close contacts of the patient are to be monitored for signs and symptoms for ten days from the last contact with a suspected case. Healthcare workers exposed to the case’s oral or respiratory secretions or exposed to their wounds should also be monitored. Prophylactic antibiotics (penicillin or erythromycin) for seven days are indicated for close contact.”
Prevention
In the Nigerian childhood immunisation schedule, three doses of pentavalent vaccine (diphtheria toxoid-containing vaccine) are recommended at the 6th, 10th, and 14th week of life.
WHO recommends a three-dose series of diphtheria toxoid-containing vaccines in the first year of life beginning at 6 weeks of age and advises that 3 booster doses of diphtheria toxoid-containing vaccine are provided during childhood and adolescence to ensure long-term protection.
In endemic settings and outbreaks, healthcare workers may be at greater risk of diphtheria than the general population. Consequently, NCDC advised that special attention should be paid to immunising healthcare workers (clinicians, laboratory scientists etc.) who may have occupational exposure to Corynebacterium diphtheriae.