Diphtheria, an acute infectious disease caused by toxin-producing strains of Corynebacterium diphtheriae, has been a longstanding global health concern, and Nigeria is no exception. This disease primarily affects the upper respiratory tract, skin, and, in rare cases, other mucous membranes. Additionally, two other bacteria, C. ulcerans and C. pseudotuberculosis, can also produce diphtheria toxin, making the disease a persistent health threat.
Humans are the primary reservoir for C. diphtheriae, although it has been found in some animals, including horses. The bacterium can survive on environmental surfaces, dust, and fomites, making it easily transmissible. In temperate climates, respiratory disease is more prevalent during the autumn/winter season, while tropical countries often experience cutaneous disease, serving as a reservoir for transmission.
Transmission occurs through inhalation of respiratory droplets, direct contact with respiratory secretions, infected skin lesions, or contaminated objects. While many nasopharyngeal infections don’t lead to active disease, transient carriage of the bacteria can persist for weeks, even in immunized individuals. Asymptomatic carriage plays a vital role in sustaining transmission.
In the pre-vaccine era, diphtheria was a significant cause of childhood morbidity and mortality. The introduction of diphtheria toxoid vaccines led to a dramatic decline in reported cases in developed countries. However, it remains endemic in countries with sub-optimal childhood vaccination rates, posing a threat to countries with strong immunization programmes but susceptible to older populations.
The global impact of diphtheria varies widely. While industrialized countries have seen a remarkable decrease in cases, large epidemics have occurred in some regions due to factors like declining vaccination rates, population mobility, delayed recognition, and limited healthcare infrastructure. Developing countries have reported declining cases since the World Health Organization’s Expanded Programme for Immunization launch in 1974, but significant disparities persist among nations.
In recent years, outbreaks have been reported in various parts of the world, including the Americas, Asia, and Africa. Waning immunity among adults and the absence of booster immunizations have increased the number of susceptible individuals, raising the risk of re-introduction and outbreaks.
Diphtheria typically presents with the formation of a tough, adherent pseudo-membrane at the site of infection. Symptoms and signs depend on the site of infection, pseudo-membrane size, duration of illness, and immunization history. Regardless of the site, systemic manifestations result from toxin absorption, making early diagnosis and treatment crucial.
The hallmark of treatment for respiratory diphtheria is the swift administration of diphtheria antitoxin, which effectively neutralizes circulating diphtheria toxin. However, it’s essential to note that this antitoxin cannot neutralize toxins bound to cells. Early administration of antitoxin during the disease’s course proves effective in reducing local disease severity, minimizing systemic complications like myocarditis and polyneuropathy, and ultimately lowering the risk of mortality.
Notably, diphtheria antitoxin remains in short supply globally, with limited or expired stockpiles in some countries. Recognizing this challenge, the World Health Organization (WHO) has taken action, recommending collaboration with partners to support antitoxin production and establish a stockpile. Furthermore, the WHO has been urged to identify mechanisms for developing alternatives to equine diphtheria antitoxin, such as monoclonal antibodies.
After treatment, it is essential to document the elimination of C. diphtheriae through consecutive negative cultures. Supportive care remains crucial during recovery, and physical therapy is recommended for patients with neuropathies to maintain range of motion in affected extremities.
Complications such as cardiac and respiratory issues can occur early in the disease course. Cardiac complications, particularly myocarditis, require close monitoring through ECGs, and prompt intervention with supportive care may be necessary. Airway obstruction can result from various causes and may require consultation with specialists for tracheostomy or intubation.
The most effective means of primary prevention against diphtheria is immunization with diphtheria toxoid. Vaccination programmes vary by age group and region but generally involve three doses in childhood, followed by boosters during adolescence and adulthood. Pregnant women are advised to receive Tdap to protect against pertussis, another vaccine-preventable disease.
Immunization strategies differ among countries, but vaccination remains the most potent tool against diphtheria. Routine booster doses and vaccination programmes are crucial to maintaining immunity and preventing outbreaks.
In Nigeria, the Nigeria Centre for Disease Control and Prevention (NCDC) has been grappling with a diphtheria outbreak that has persisted since December 2022. This alarming outbreak has now claimed the life of a four-year-old child in the Federal Capital Territory (FCT), Abuja, in June 2023. The NCDC reported a total of 798 confirmed diphtheria cases across eight states and the FCT by the end of June 2023, with the majority of cases concentrated in Kano. Tragically, 80 deaths have been recorded, resulting in a case fatality rate of 10.0%. The outbreak primarily affects children aged 2 to 14 years, and a significant proportion of cases, 82%, were unvaccinated.
The outbreak’s main driver is historically sub-optimal vaccination coverage, with less than half of children under 15 years old being fully protected against diphtheria. The NCDC is working diligently with the FCT Health and Human Services Department to implement control measures and contain the spread of the disease. They urge the public to stay vigilant and seek medical attention promptly if they exhibit symptoms of diphtheria, as early diagnosis and treatment are crucial for a positive outcome. Healthcare workers are also encouraged to report suspected cases promptly.
In response to the outbreak, the NCDC activated a multi-sectoral national Diphtheria Emergency Operations Centre, coordinating surveillance and response activities across the country. This includes establishing technical working groups, deploying rapid response teams, and supporting the establishment of incident management systems in affected states. Surveillance tools and guidelines have been developed and disseminated, while healthcare workers have received training on diphtheria presentation, prevention, and surveillance.
Laboratory capacity has been strengthened for diphtheria diagnosis, including training of laboratory personnel and the supply of essential materials. The country has procured and prepositioned diphtheria antitoxin for the first time in decades, distributed to affected states. Standard Operating Procedures for antitoxin use have been developed, and isolation wards have been established in key areas.
To mitigate the risk of diphtheria, the NCDC advises parents to ensure their children receive the three doses of diphtheria-containing pentavalent vaccine as part of Nigeria’s childhood immunization schedule. Healthcare workers should maintain a high index of suspicion for diphtheria and practice infection prevention and control measures. Individuals with symptoms suggestive of diphtheria should isolate themselves and notify relevant health authorities promptly. Close contacts of confirmed cases should be closely monitored, receive antibiotic prophylaxis, and start treatment as needed. Additionally, healthcare workers with significant exposure to diphtheria cases should be vaccinated against the disease.
The diphtheria outbreak in Nigeria underscores the critical importance of vaccination and public health measures to prevent vaccine-preventable diseases. Timely intervention and a coordinated response are essential to curbing the spread of diphtheria and protecting vulnerable populations.
Okeke writes from the Centre for Social Justice (CSJ) Nigeria
