Epidemiology

Expanded vaccination strategies have substantially reduced the worldwide burden of diphtheria; however, disease continues to be reported and global incidence has been increasing. In 2018 and 2019, 16,991 and 22,986 cases were reported, compared with 8819 cases in 2017.[8][9]​​​​​​​ In 2021 and 2022, 8638 and 9802 cases were reported.[9] The apparent decline since 2020 may be the effect of the COVID-19 pandemic on public health reporting systems, and higher notifications are anticipated in some settings post-pandemic.[10][11]​​​​​​​​​​​​​​ Disease is endemic to many regions around the world: Haiti and the Dominican Republic; Asia and the South Pacific; Eastern Europe; and the Middle East.[12][13]​ Generally, diphtheria is under-reported from many regions including Asian, African, and Mediterranean countries.[8]​ Since July 2023, at least five countries in the African region (Guinea, Mauritania, Niger, Nigeria, and South Africa) have recorded an unusual increase in cases of diphtheria and are experiencing ongoing active outbreaks.[14]

In May 2024, the Centers for Disease Control and Prevention (CDC) reported a rise in non-toxigenic C diphtheriae infections in Washington, US, increasing from 17 cases between 2012 and 2017 to 179 cases between 2018 and 2023, with factors like unstable housing and recent illicit substance use disproportionately represented among patients.[15] In June 2024, two case reports of toxigenic C ulcerans infection in humans, alongside concurrent infections in their household pets, were documented in the US.[16]

Diphtheria can affect any age group, especially people who are not fully vaccinated with diphtheria toxoid vaccine.[12]​ Population vaccination coverage of >85% confers herd immunity to diphtheria. The standard vaccine schedule is a primary three-dose series, followed by boosters during childhood and adolescence. Low booster rates lead to declining diphtheria antitoxin concentration over time.[17] In 2022, global coverage for the third dose of the diphtheria-tetanus-pertussis-containing vaccine (DTPcv3) reached 84%. However, this coverage varied across regions, ranging from 72% to ≥94%.[18]​​​ Diphtheria outbreaks in Nigeria in 2011 and South Africa in 2015 were associated with low primary vaccination or booster rates.[19][20]

Between 2015 and 2018, diphtheria outbreaks were reported in Haiti, Venezuela, and Yemen.[13][21]​​​​​​​ In 2018-19, the largest outbreak of the current century developed among displaced Rohingya refugees in Kutupalong camp, Cox’s Bazar, Bangladesh, with up to 9000 cases, but a low mortality rate of 0.5%.[21][22][23]​​​​​​

In the UK in 2022 and 2023, there was an increase in cases of diphtheria among asylum seekers arriving from a range of locations. This mirrors a wider situation across a number of European countries.[24][25][26]

Use of this content is subject to our disclaimer