Methaemoglobinaemia following ingestion of a commonly available food additive

In 2006, at Liverpool Hospital in Syd-ney, two separate clusters of patientspresented to the emergency depart-ment with cyanosis after consuminghome-prepared food to which sodiumnitrite had been added.In the first cluster, a husband andwife of Vietnamese–Chinese origindeveloped cyanosis and dyspnoea afterconsuming homemade rice cakes con-taining “Nutre Powder” and “BoraxPowder”, which were commonly avail-able from local Asian food stores in thearea. Both patients arrived by ambu-lance and, despite oxygen therapy,remained cyanotic. Their blood sam-ples had a distinctive chocolate brownappearance, and laboratory testingconfirmed methaemoglobinaemia. Thehusband, who was the more unwell,had a measured methaemoglobin levelof 57%. After treatment with intrave-nous methylene blue, his conditionrapidly improved. The wife, who had amethaemoglobin level of 21%, was treated supportively with oxygenand monitored closely. Both patients were admitted to the intensivecare unit for a brief period of observation before being transferred tothe haematology unit. Their subsequent progress was uneventful, andboth patients were discharged from hospital 2 days later.On request from medical staff, the couple brought into the hospitalthe two packets used, both containing whitish powder. The first waslabelled “Goldfish” brand “Borax” and the second, “Goldfish” brand“Nutre Powder” (Box). No further information about the contents wasprinted on the packaging. The packets were imported through aspecialty Asian food distributor based in Melbourne, and the wifeclaimed they were commonly available food additives. She had usedboth ingredients in the meal she prepared that evening from a recipegiven to her by her mother. She also claimed her mother hadpreviously used the products in China without incident. Neitherpatient knew the composition of the products, and questioning of theproduct’s importer by the medical team yielded no further informa-tion.Two weeks later, a second cluster of three new cases, involving aVietnamese family unrelated to the index cases, presented to LiverpoolHospital emergency department withidentical symptoms after eating a porkdish prepared using an unidentified whitepowder. Laboratory testing again con-firmed methaemoglobinaemia, with levelsranging from 39% to 51%. Intravenousmethylene blue was administered, leadingto rapid clinical improvement. All threepatients made uneventful recoveries afterbeing observed in the emergency depart-ment overnight and were released fromhospital the next day.In both clusters, the onset of initialsymptoms, such as vomiting, shortness ofbreath and dizziness, was dramatic, withinminutes of consuming the contaminatedfood preparations. In the second cluster,two family members who had eaten thecontaminated pork dish noticed thesymptoms just after leaving home. Theycalled back to warn the others that thefood might be contaminated, but the oth-ers had already consumed the dish as well.A fourth person in that cluster alsobecame ill, but had much less severesymptoms, having eaten only a small amount. She was seen byparamedics but not transported to hospital with the others. On reviewby her local doctor the next day, she had made a full recovery.Investigation by the New South Wales Food Authority and staff ofthe Public Health Unit of Sydney South West Area Health Servicefound that identical Goldfish brand Nutre Powder had been used infood consumed by the patients in the second cluster, reportedly as aflavour enhancer. The packages were purchased from separate localretailers. Importantly, this group was found not to have been exposedto any other known causes of methaemoglobinaemia. Residual NutrePowder from both clusters and Borax Powder from the first clusterwere submitted to the Division of Analytical Laboratories in Lid-combe, Sydney, for testing. Those labelled Nutre Powder contained100% sodium nitrite, while the packet labelled Borax contained 100%sodium tetraborate.On the day that laboratory results on the additives used by the firstcluster patients became available, NSW Health alerted hospital emer-gency departments and the public to the risk of methaemoglobin-aemia associated with ingestion of Nutre Powder. As Goldfish brandNutre Powder was imported via Victoria, the Victorian Department of