Diphtheria case reported in NT: What you need to know
July 11, 2023
Recent diphtheria case reported
A 32-year-old Indigenous woman from Far North Queensland with poorly controlled type 2 diabetes and no recent travel history, presented to a local clinic with a day-old history of painful swallowing. Despite being vaccinated against diphtheria five times during her childhood and adolescence, with her last shot 13 years prior, her symptoms worsened over time. Initially misdiagnosed as streptococcal pharyngitis, her condition escalated with a visibly swollen neck, impaired speech, and greyish throat plaques. Upon transfer to the hospital, respiratory diphtheria was suspected and confirmed through a throat swab and PCR test, revealing the presence of toxigenic Corynebacterium diphtheriae.
Her treatment regimen included antibiotics and diphtheria antitoxin, along with standard plus droplet precautions. Though her throat symptoms improved by day 3, cardiac complications emerged, manifesting as a prolonged QT interval and elevated cardiac troponin levels despite no significant chest pain or breathlessness. Further investigation identified myocarditis, a common complication of diphtheria, while her throat culture tested negative after 14 days of treatment. After being hospitalised for 25 days, the patient was discharged and later received a diphtheria-tetanus vaccine, 33 days after the administration of diphtheria antitoxin.
Read through this case report in full at: https://www.mja.com.au/journal/2023/218/10/locally-acquired-respiratory-diphtheria-australia
What do we know about diphtheria
Once listed among the leading causes of mortality in children, diphtheria accounted for over 4,000 fatalities in Australia between 1926 and 1935. The landscape significantly changed with the advent of toxoid-containing vaccines worldwide in the 1940s, leading to a precipitous drop in diphtheria instances. Presently, diphtheria has become a rare occurrence. Until the recent identification of two cases in NSW, Australia had not reported any instances of respiratory diphtheria in children since 1992. In the span from 2011 to 2019, the country noted 38 cases of cutaneous diphtheria impacting both children and adults. During this same timeframe, seven adult cases of respiratory diphtheria were recorded. Tragically, two of these patients, both unvaccinated adults, succumbed to respiratory diphtheria in 2011 and 2018, respectively. So why is it back again?
The collaborating organisations revealed that a staggering 23 million children worldwide did not receive their scheduled childhood immunizations in 2020. The routine process of childhood vaccination has been recently impeded due to the global COVID-19 pandemic and ongoing conflicts in countries like Ukraine, Ethiopia, Somalia, and Afghanistan. As of April 1, a total of 57 vaccination drives internationally, aimed at preventing certain diseases, which were supposed to have been conducted since the pandemic began, remain in suspension in 43 nations. This delay affects roughly 203 million individuals, the majority of whom are children. Among the postponed campaigns, 19 are for measles, thereby putting 73 million children at potential risk of contracting measles due to skipped vaccinations.
Based on reports from the World Health Organization (WHO) and the United Nations Children’s Fund (UNICEF), it is clear that achieving a coverage of 95% or higher with two doses of the routine childhood vaccines such as measles and diphtheria-tetanus-acellular pertussis can guard against the disease. Warnings are in place for primary healthcare to monitor the decline in this vaccination rate due to the pandemic as new resurgences occur for preventable diseases such as diphtheria and measles in Australia.
Pathogenesis of diphtheria
Diphtheria, an intense bacterial malady, is precipitated by strains of Corynebacterium diphtheriae that are adept at generating toxins. The bacterium is gram-positive, non-spore-forming and non-capsulate. The name of the disease is derived from the Greek diphtheria, meaning ‘leather hide.’ The distinguished physician Hippocrates provided the first known descriptions of this disease in the 5th century BCE, with subsequent accounts of epidemics chronicled by Aetius in the 6th century AD.
The bacteria produce an exotoxin that acts locally on the mucous membranes of the respiratory tract or, less commonly, on damaged skin. It produces an adherent pseudomembrane. Systemically, the toxin acts on cells of the myocardium, nervous system and adrenals. Diphtheria has the potential to affect nearly any mucous membrane. Among unvaccinated individuals, pharyngeal diphtheria is the most prevalent form of the illness. It is marked by an inflammatory discharge that forms a grey or green membrane in the upper respiratory tract, potentially leading to acute, severe respiratory blockage. Serious complications that can arise from diphtheria include myocarditis and neuritis, with the latter typically impacting motor nerves. Over the past 30 years, the fatality rate linked to diphtheria cases has been as high as 16% in Australia.
Diphtheria antitoxin, first introduced in the 1890s, neutralises the unbound toxin. The primary treatments for diphtheria today are antibiotics and antitoxin, but these interventions may not always yield success. The sole effective method to secure protection against diphtheria is through active immunisation using diphtheria-inclusive vaccines.
Up-to-date immunisations are key
The requisite antitoxin levels in the bloodstream needed to ward off diphtheria have been well established:
- Antitoxin levels below 0.01 IU/mL offer limited protection.
- Levels ranging from 0.01–0.1 IU/mL typically ensure protection.
- When levels surpass 0.1 IU/mL, they afford a more guaranteed and extended protective period.
Research indicates that following the three-dose primary immunisation sequence of DTPa-hepB-IPV-Hib, between 97.4–100% of infants exhibited diphtheria antitoxin levels of 0.1 IU/mL or higher. Post the fourth dosage during the second year, 96.8–100% of infants should show antibody concentrations of 0.1 IU/mL or higher for both diphtheria and tetanus.
An investigation involving adults with an unclear vaccination history demonstrated that after receiving three doses of either a dT or dTpa vaccine, 99% of adults possessed antibody levels indicative of protection.
Regarding the longevity of immunity, comprehensive immunisation elicits protective antitoxin levels that endure throughout childhood. However, by middle age, a minimum of 50% of individuals who haven’t received vaccination since childhood present levels below 0.1 IU/mL. These findings have been corroborated by a national serosurvey in Australia. The clinical implications of these antibody levels in terms of protective immunity remain ambiguous.
Within six weeks, a singular low dosage of diphtheria toxoid can provoke protective antitoxin levels in adults who have been previously immunised, and may be the answer to preventing any further outbreak of disease following the pandemic years.
The role of GPs
Early identification and prevention of the spread of vaccinable diseases demand a multipronged approach. Foremost, maintaining a high index of suspicion for these diseases, particularly in patients who present with symptoms consistent with such illnesses, is vital. Given the global nature of our communities, it’s important to consider travel histories and potential exposure risks, as many vaccinable diseases are more prevalent in specific regions of the world.
Continuous education is a crucial element for early detection. Staying abreast of the most current knowledge on symptomatology, disease progression, and diagnostic methodologies for vaccine-preventable diseases is essential. This includes understanding the various presentations of diseases like diphtheria and the antitoxin levels that provide protection against them.
Prevention remains the best strategy for controlling the spread of these diseases. Hence, promoting and administering vaccinations as per guidelines to all eligible patients is a priority. This involves ensuring that your patients are up-to-date with their vaccination schedules and are adequately informed about the importance of vaccinations.
It’s also essential to identify at-risk patients who may not have received their childhood vaccinations, or whose immunity may have waned, such as elderly patients, those looking to travel to diphtheria prevalent areas or those with an unknown vaccination history. Consider whether they might benefit from booster doses or catch-up immunisation programs.
Furthermore, quick isolation of suspected cases, appropriate referrals, and timely reporting to public health authorities can help prevent wider outbreaks. Also, encouraging patients to engage in preventive behaviours such as maintaining good hygiene and avoiding contact with infected individuals can aid in halting the spread of diseases.
For more information on your role in the disease, revisit the guidelines from Australian Government Department of Health and Aged Care – Australian Immunisation Handbook at: https://immunisationhandbook.health.gov.au/
Department of Health and Aged Care (2023) The Australian Immunisation Handbook. Available at: https://immunisationhandbook.health.gov.au/.
Smith, S. et al. (2023) Locally acquired respiratory diphtheria in Australia, The Medical Journal of Australia. Available at: https://www.mja.com.au/journal/2023/218/10/locally-acquired-respiratory-diphtheria-australia.
CDC (2022) Diphtheria, Centers for Disease Control and Prevention. Available at: https://www.cdc.gov/vaccines/pubs/pinkbook/dip.html#:~:text=Diphtheria%20is%20an%20acute%2C%20bacterial,6th%20century%20AD%20by%20Aetius.