A petrol additive explained 82 cases of near-fatal methaemoglobinaemia

Design

coordinated clinical and toxicological outbreak investigation

Population

82 patients with severe acquired methaemoglobinaemia, 90% male, median age 22.5 years

Primary outcome

identification of the causative agent, with clinical course described

Effect

N-methylaniline or metabolites in 37 of 39 tested (95%); median methaemoglobin 44.6%; two deaths

Clinicians in Lampedusa began seeing severe acquired methaemoglobinaemia with no apparent cause among migrants disembarking from Central Mediterranean crossings. A coordinated clinical and toxicological investigation collected 82 cases between March 2024 and December 2025, 90% male, median age 22.5 years. Median methaemoglobin at presentation was 44.6% (IQR 32.0 to 55.7), and 43% presented at 50% or above.

Toxicology identified N-methylaniline, a petrol additive, or its metabolites in 37 of 39 patients tested (95%), and found it at 1.1% concentration in a fuel sample taken from one of the implicated vessels. The mechanism is prolonged dermal absorption from fuel-contaminated seawater pooling on the floor of overcrowded boats. Methylene blue was used in 90% of patients, often repeatedly. Haemolytic anaemia appeared as a delayed complication in 38 patients and frequently required transfusion. Two patients died.

The generalisable lesson is about the presentation rather than the setting. Severe methaemoglobinaemia looks like refractory hypoxaemia: cyanosis that does not improve with oxygen, a pulse oximeter that will not move, and an arterial oxygen tension that looks normal. Any occupational or environmental setting with prolonged skin contact with fuels or aniline dyes can reproduce it — and in those settings the survivable version of this story depends on methylene blue being on the shelf and someone thinking of it.

• Suspect methaemoglobinaemia when cyanosis does not respond to oxygen and the arterial oxygen tension is normal
• Request co-oximetry — a standard pulse oximeter cannot make this diagnosis
• Take an exposure history covering fuels, aniline dyes, and topical or ingested oxidising agents
• Check methylene blue is stocked where it would be needed, and know the dose before you need it
• Watch for delayed haemolysis after the methaemoglobin is corrected — it appeared in nearly half this cohort

Why it matters

It names an exposure route — dermal absorption of a fuel additive — that a standard poisoning history would not ask about.

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