Anaphylaxis in a milk-allergic child after ingestion of soy formula cross-contaminated with cow's milk protein

In this report we describe a 9-month-old boy with severe persistent asthma and documented cow's milk allergy (presented with eczema and severe systemic reactions) who had an anaphylactic reaction to a soy formula contaminated with cow's milk protein. Quantitative enzyme-linked immunosorbent assay analysis revealed trace quantities of ß-lactoglobulin in the offending soy formula as well as the dry powder. The patient did not demonstrate clinical reactivity to soy protein (negative challenge, tolerated pure soy formula well). Cross-contamination of the offending soy formula was presumed to have occurred during food manufacturing. This case demonstrates that trace quantities of cow's milk protein can elicit severe systemic reactions in highly milk-allergic individuals. This infant ingested the equivalent of 0.4 mL of cow's milk from the soy formula as documented by an immunoassay for ß-lactoglobulin. This highlights the ease with which cross-contamination can occur during food processing and reinforces the need for better quality control.