An outbreak of diphtheria, a serious disease that is especially harmful to children, has been confirmed in Nigeria. But what is diphtheria, and what leads to its spread?
The agency that tackles public health emergencies in Nigeria has raised the alarm over an outbreak of diphtheria, a serious bacterial infection.
In an advisory on 20 January 2023, the Nigeria Centre for Disease Control (NCDC) said it was monitoring cases in four states, where all 123 cases so far have been confirmed.
As of 22 January these states were Kano (with an outbreak of 100 cases), Yobe (17), Lagos (5) and Osun (1).
Diphtheria is one of the most feared childhood diseases, marked by devastating outbreaks, according to the World Health Organization (WHO).
In this factsheet, we take a closer look at the disease, the role that immunisation plays in containing its spread, and what health officials are doing to counter the outbreak in Nigeria.
What is diphtheria?
Diphtheria is a highly contagious infection that is often fatal in up to to 10% of cases. It is caused by the bacterium Corynebacterium diphtheria, of which humans are the only natural host.
It affects all age groups but mostly young children.
Diphtheria is endemic in countries with low immunisation levels. This means it is consistently present but limited to a particular region and makes it easier to predict its behaviour.
The disease has been reported in many countries and in various regions, from Eastern Europe, Southeast Asia and South America to the Indian subcontinent.
It occurs less often in higher-income countries. As of 19 January, there were at least 391 cases of the disease in nine countries - Austria, the Czech Republic, France, Germany, Italy, the Netherlands, Norway, Switzerland and the United Kingdom.
How is diphtheria transmitted and what are its symptoms?
Diphtheria is transmitted through respiratory secretions, or by breathing in droplets from an infected person when they cough or sneeze.
Most infections do not show symptoms or are mild. For those that do, symptoms usually start two to five days after someone becoming infected, Dr Adeboye Muhammed, an associate professor of paediatrics and child health at the University of Ilorin in western Nigeria, told Africa Check.
"You have a sore throat, low fever, nasal discharge, and swollen glands in the neck," he said.
The disease produces toxins which kill healthy respiratory system tissue. The dead tissue forms a membrane that can build up over the throat and tonsils, making breathing and swallowing difficult. Many patients die from airway obstruction.
The US Centers for Disease Control and Prevention (CDC) says "if the toxin gets into the bloodstream, it can cause heart, nerve, and kidney damage".
Where the disease is coupled with poor hygiene, infection of the skin is also common, leading to pus-filled blisters, including on the legs and hands.
The CDC notes that "people can also get sick from touching infected open sores or ulcers".
Who is at risk from diphtheria?
There is a higher risk of spread of the disease in closed and crowded spaces. Communities with high vaccination rates have a lower risk.
Healthcare workers are also at increased risk in endemic settings and during outbreaks, the WHO says.
According to the global health agency, diphtheria is treated with an antitoxin. Antibiotics are also given to eliminate bacteria and toxin production and to prevent transmission.
The CDC says infected people cannot infect others 48 hours after they begin taking antibiotics. "However, it is important to finish taking the full course of antibiotics to make sure the bacteria are completely removed from the body," the CDC says.
Children should also be immunised against diphtheria. A three-dose vaccine during infancy helps build lifelong immunity to diphtheria, according to the NCDC. In Nigeria this is given in the sixth, 10th and 14th week of life.
Diphtheria vaccines, together with those for tetanus and pertussis, all together known as DTP, have been part of the WHO's immunisation programme since 1974. The agency says the diphtheria vaccine, which is made by modifying the toxin, "is one of the safest vaccines available".
Many countries, including Nigeria, give two more vaccines to form the pentavalent vaccine. This protects a child from five life-threatening diseases: diphtheria, pertussis or whooping cough, tetanus, Hepatitis B and type B Haemophilus influenzae or Hib disease.
Outbreaks in Nigeria since 2011 show immunisation gaps
Diphtheria outbreaks tend to reflect insufficient vaccination coverage.
In 2011, there was an outbreak in the north-eastern Nigerian state of Borno, where 98 cases were reported. This led to 21 deaths.
The NCDC attributed the outbreak and the high fatality rate to low vaccination coverage and delays in diagnosis. The absence of antitoxin and antibiotics for treatment in health facilities was also a factor.
Health experts have said the 2023 outbreak in Nigeria was caused by the widening gap in immunisation coverage.
Dr Rotimi Adesanya is a fellow at the Academy of Public Health in Nigeria's capital, Abuja. Low coverage was "common in the northern part of Nigeria, villages and hard-to-reach areas", he told Africa Check.
Nigerian authorities should strengthen coverage in the north and include private hospitals in its immunisation system, he added.
Data showed early warnings signs
Nigeria's most recent immunisation data was published in 2022. It showed stark coverage gaps.
In August 2022, the National Bureau of Statistics and other health partners released the 2021 Multiple Indicator Cluster Survey (Mics) and the National Immunisation Coverage Survey (Nics).
The multi-indicator survey provides data on, among other subjects, child mortality, health, education and sanitation and hygiene, while the Nics assesses vaccination coverage.
A total of 41,532 households were sampled nationally for the Mics, and 6,740 households for the immunisation survey.
The immunisation survey showed that only 56.6% of children between ages 12 and 23 months had received the third dose of DTP at any time before the survey. This rose slightly to 57.9% in children of ages 24 to 35 months.
Immunisation records were used to inform questions around coverage.
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Children in the northeast geographical zone had the lowest immunisation rate for diphtheria, with 41.7%. The rate was 42.9% in the northwest and 57.2% in the north-central region of the country.
In urban areas, more children (72.7%) had received the third DPT dose, compared to 47.5% in rural areas. The proportion was also higher - 88.9% - in children born to mothers who had higher or tertiary education, against just 36.2% in mothers with no education.
Diphtheria vaccination rates were also high in children of households regarded as rich - 84.6% - against 38.7% in the poorest households.
What health agencies are doing
The NCDC says it is supporting states with antitoxins for the treatment of confirmed cases of diphtheria, and that it is also working with scientists to increase the diagnostic capacity for diphtheria.
NCDC advice on reducing risk of diphtheria infection includes:
Vaccinate children and all healthcare workers with a high level of exposure.
Isolate cases of individuals with signs and symptoms of diphtheria.
Always practise standard precautions while handling patients and body fluids.
Dr Faisal Shuaib is the executive director of Nigeria's National Primary Health Care Development Agency. He told the media in January 2023 that the outbreak was an indicator of poor immunisation coverage in the affected states.
The agency, which has deep reach in the community, was planning a mass vaccination campaign in populations identified to be at risk, he said.
Nigeria would continue to use the pentavalent vaccine to prevent further outbreaks of diphtheria, he added.
