A Box plots showing OD values of 1∶100 diluted sera from Ghanaian BU patients (n = 96) and control individuals (n = 384) tested in an anti-M. ulcerans 18 kDa shsp IgG specific ELISA. B Boxplot showing the distribution of OD values for BU patients and control individuals for different age groups. No IgG titres above the background level were observed for children below the age of 5 years. The background response (OD<0.35) is indicated as a dotted line. C Sera from eight 2-year-old children were tested by Western Blot analysis to reconfirm the absence of anti-M. ulcerans 18 kDa shsp IgG. An ELISA positive control serum (OD = 0.76) was included (+) flanking the tested sera.