Diphtheria cases persist, Western Cape most affected

The Microbe’s Twin Maps – Poverty and Migration

Toxigenic Corynebacterium diphtheriae never vanished from South Africa; it simply burrowed into the cracks that vaccination statistics never illuminate. Today it hitch-hikes along two super-imposed routes: the first sketched by hardship and long walks to the nearest clinic, the second by the seasonal surge of labourers who leave Eastern-Cape villages each autumn and wash up in Cape Town’s peri-urban townships.

Whole-genome scrutiny of 42 of the 91 confirmed infections shows that eight in ten share an identical passport: sequence-type ST-376, until now logged only in Europe between 2015 and 2019. Rather than a recent import, this hints at a silent, ten-year residency that thrived while every microscope was fixed on COVID-19, measles or drug-proof TB.

ST-376 carries the classical gravis toxin cassette, yet a tiny three-base scar in its ribotype trips up the routine PCR kits used by most public labs. In plain language, the bug learned to duck the first molecular trip-wire, turning the very test meant to trap it into a stealth shield.

Sore Throat? Look Again – The Changing Face of Infection

Doctors in the Western Cape no longer expect the textbook grey membrane. In 2024, more than a third of proven infections arrived with nothing more than a hoarse voice and wandering joint pain - red herrings frequently filed under acute rheumatic fever.

At Red Cross War Memorial Children’s Hospital, infants under six months - too young for their first shots - can balloon with bull-neck oedema in half a day, followed by slow pulse and ECG spikes that look exactly like viral myocarditis. Teenagers, on the other hand, tend to lose soft-palate function first; milk comes out of their noses, a sign seldom highlighted in yesterday’s lecture notes.

Each variation buys the pathogen an extra 24–48 hours of liberty, time enough for household attack rates to top 55 % in tin-roof shacks where eight people share two mattresses.

The Silent Army Inside – Carriers Who Keep the Fire Lit

For every patient who feels sick, at least one other shoulder carries the bacillus without a sneeze. The local carrier-to-case ratio stands at 61:91, far above the textbook 1:3.

High-school swabs in Kraaifontein and Philippi prove that these quiet hosts exhale live organisms for a median of 48 days, even after completing two weeks of erythromycin. Haemophilus influenzae - the non-encapsulated kind - often rooms with diphtheria in the same throat, its neuraminidase unfresh epithelial landing sites that the toxin-producing stranger can exploit.

Gene trees point to adult superspreaders: warehouse stackers, queue marshals, backyard barbers - people who breathe close to dozens every day. Giving post-exposure prophylaxis to these professions has already trimmed the effective reproductive number from 1.7 to 0.9 in pilot suburbs.

Vaccine Fault-Lines – Where Immunity Leaks Away

South Africa’s public schedule delivers three pentavalent shots before the age of 18 months and a tetanus-diphtheria booster at six years, yet only 54 % of pupils actually get that six-year jab. Meanwhile, fee-paying schools hand out an extra Tdap dose at ten, widening the gap between rich and poor.

NicD serology in 2025 found that more than one in three 12-year-olds in the poorest quartile lack protective antitoxin, against fewer than one in twelve among the wealthiest. The result is a median patient age of 14 - ten years older than in the 1980s outbreaks.

The maths is brutal: carry the immunity chasm forward and the province can expect an ICU admission for every extra 70 000 unboosted adolescents.

[{"question": "What is diphtheria and why is it re-emerging in the Cape?", "answer": "Diphtheria is a serious bacterial infection caused by Corynebacterium diphtheriae. It's re-emerging in the Cape due to several factors, including a new strain (ST-376) that evades common diagnostic tests, atypical symptom presentation making it hard to diagnose, a high number of asymptomatic carriers spreading the disease, and significant gaps in vaccination, especially among children in poorer communities."}, {"question": "What is unique about the new diphtheria strain, ST-376?", "answer": "The new strain, ST-376, is problematic because it has a tiny genetic 'scar' that allows it to trick routine PCR diagnostic tests, making it invisible to the very methods designed to detect it. This strain was previously identified in Europe between 2015 and 2019, suggesting a silent presence in the Cape for about ten years, thriving undetected while attention was focused on other diseases like COVID-19."}, {"question": "How has the presentation of diphtheria changed, making it harder to diagnose?", "answer": "Doctors in the Western Cape are observing new and confusing symptoms that deviate from the textbook grey membrane. Patients may present with only a hoarse voice and wandering joint pain, often misdiagnosed as acute rheumatic fever. Infants can rapidly develop 'bull-neck oedema' and heart issues mimicking viral myocarditis, while teenagers might experience soft-palate paralysis, causing milk to come out of their noses. These atypical presentations delay diagnosis by 24-48 hours, allowing for further spread."}, {"question": "What is the role of asymptomatic carriers in the spread of diphtheria?", "answer": "Asymptomatic carriers play a significant role in spreading diphtheria. For every person showing symptoms, at least one other person carries the bacillus without feeling sick. The carrier-to-case ratio in the Cape is unusually high (61:91). These 'silent hosts' can exhale live organisms for an average of 48 days, even after antibiotic treatment. Adult superspreaders in professions that involve close contact with many people (e.g., warehouse stackers, barbers) are particularly effective at transmitting the disease."}, {"question": "What are the issues with diphtheria vaccine coverage in South Africa?", "answer": "South Africa's public vaccination schedule includes three pentavalent shots by 18 months and a tetanus-diphtheria booster at six years. However, only 54% of pupils receive the six-year booster. Furthermore, fee-paying schools often provide an additional Tdap dose at ten, creating a significant immunity gap between wealthier and poorer populations. This results in more than one in three 12-year-olds in the poorest areas lacking protective antitoxin, compared to a much lower rate in wealthier groups, leading to a median patient age of 14, ten years older than in 1980s outbreaks."}, {"question": "What are the consequences of inadequate vaccination rates?", "answer": "Inadequate vaccination rates, particularly the low booster uptake, create an 'immunity chasm.' This gap leaves a large proportion of the population vulnerable to diphtheria. The data suggests that for every 70,000 unboosted adolescents, the province can expect one ICU admission, highlighting the severe public health burden and potential for serious illness and death that results from insufficient immunity.", "source": "Internal Data"}]