The Nigeria Centre for Disease Control and Prevention (NCDC), Nigeriaâ€™s national public health institute with the mandate to coordinate/lead emergency preparedness and response to public health threats due to communicable diseases, has been responding to and monitoring a Diphtheria outbreak in some parts of the country.
Over the past five decades, the incidence of diphtheria has reduced dramatically worldwide because of widespread immunisation using a diphtheria toxoid-containing vaccine. The number of Diphtheria cases reported to the World Health Organization (WHO) declined from about 100,000 cases in 1980 to less than 10,000 cases in 2021. However, in recent years, there has been a gradual rise in cases with over 20,000 cases recorded in 2019. Diphtheria is primarily controlled by the prevention of infection through high population immunity achieved by high vaccination coverage. Consequently, Diphtheria outbreaks reflect inadequate vaccination coverage.
In Nigeria, there was an outbreak in Borno, north-eastern Nigeria in 2011 with a total of 98 cases, and 21 deaths (case fatality ratio was 21.4%). This outbreak and the associated high case fatality were due to a combination of low vaccination coverage, delayed clinical recognition and laboratory confirmation, and the absence of antitoxin and antibiotics for treatment.
Diphtheria is a severe bacterial disease caused by the bacterium Corynebacterium species, mainly by toxin-producing Corynebacterium diphtheriae and rarely by toxin-producing strains of C. ulcerans and C. pseudotuberculosis. It manifests as laryngitis, pharyngitis or tonsillitis and is associated with the presence of an adherent membrane covering the tonsils, pharynx and/or nose. Beyond the respiratory symptoms, approximately a quarter of cases may develop heart problems (myocarditis). The mainstay of Diphtheria treatment is antibiotics and Diphtheria antitoxin (DAT).
Diphtheria spreads easily between people by direct contact or through the air through respiratory droplets from coughing or sneezing. 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.
The most common type of diphtheria is classic respiratory diphtheria. The onset of signs and symptoms is usually from 2 â€“ 5 days (could be as high as 10 days) after exposure. Initial symptoms may be mild and include fever, runny nose, sore throat, cough, and red eyes (conjunctivitis). In severe cases, 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 in part due to enlarged lymph nodes and may 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.
Complications due to diphtheria usually 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%), 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). Case fatality ratios up to 10% have been reported in diphtheria outbreaks and are higher in settings where diphtheria antitoxin (DAT) is unavailable.
Clinical diagnosis of diphtheria usually relies on the presence of 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.
Two samples should be collected from every suspected case at first contact with the case - a pharyngeal swab and a nasal swab â€“ 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 2â€“8oC. 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 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.
Suspected case: Any person with an illness of the upper respiratory tract characterized by the following: Pharyngitis, nasopharyngitis, tonsillitis or laryngitis AND adherent pseudo-membrane of the pharynx, tonsils, larynx and/or nose.
Laboratory confirmed case: A person with Corynebacterium spp. isolated by culture and positive for toxin production, regardless of symptoms.
Diphtheria is one of the priority diseases in Nigeria requiring immediate reporting and as such all suspected cases of diphtheria picked by healthcare workers in a health facility are required to be reported to the respective Local Government Area (LGA) Disease Surveillance and Notification Officer (DSNO) either directly or through the health facility surveillance focal person depending on what is obtainable within the health facility. Reports from the health facility are expected to reach the LGA DSNO within 24 hours. The LGA DSNO in turn reports the case to the state epidemiologist who then reports to NCDC.
Diphtheria infection is treated with the administration of a diphtheria antitoxin (DAT), administered intravenously or through an intramuscular injection. Antibiotics can 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 10 days from the last contact with a suspected case.
Healthcare workers exposed to the caseâ€™s oral or respiratory secretions or exposed to their wounds should also be monitored. Prophylactic antibiotics (penicillin or erythromycin) are indicated for close contact for seven days.
In the Nigeria childhood immunisation schedule, 3 doses of pentavalent vaccine (diphtheria toxoid-containing vaccine) are recommended at the 6th, 10th, and 14th week of life. WHO recommends a 3-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, special attention should be paid to immunizing healthcare workers (clinicians, laboratory scientists etc.) who may have occupational exposure to Corynebacterium diphtheriae.
Public Health Advisory
To reduce the risk of diphtheria, the NCDC offers the following advice to healthcare workers and the public:
1. Parents should be advised to ensure that their children are fully vaccinated against diphtheria with the prescribed 3 doses of a pentavalent vaccine.
2. Healthcare workers should maintain a high index of suspicion for diphtheria i.e., be vigilant and look out for symptoms of diphtheria.
3. Once a clinical diagnosis of diphtheria is made, a laboratory test should be done immediately to confirm the suspected cases. Please send samples to your State and/or NCDC National Reference Laboratory campuses in Abuja or Lagos for diagnosis.
4. Cases of individuals with signs and symptoms suggestive of diphtheria should be notified to the appropriate surveillance officer and managed in an isolation ward.
5. Practice standard precautions always while handling patients and body fluids i.e., always wear Personal Protective Equipment (PPE) irrespective of the patientâ€™s provisional diagnosis.
6. All healthcare workers (doctors, nurses, laboratory scientists, support staff etc.) with a high level of exposure to cases of diphtheria should be vaccinated against diphtheria.
The Nigeria Centre for Disease Control and Prevention (NCDC) is the countryâ€™s national public health institute, with the mandate to lead the preparedness, detection, and response to public health emergencies. The Bill for an Act to establish NCDC was signed into law in November 2018 by President Muhammadu Buhari. The mission of the NCDC is â€˜To protect the health of Nigerians through evidence-based prevention, integrated disease surveillance and response, using a One Health approach, guided by research, and led by a skilled workforce.
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Dr Ifedayo Adetifa
Nigeria Centre for Disease Control and Prevention.