Co-infection was investigated by serological screening for HIV (0/67, 0% reactive), strongyloidiasis (9/69, 13% reactive, of which four were borderline weakly reactive ELISAs of uncertain clinical significance), hepatitis B (1/22, 5% anti-Hb core positive), hepatitis C (0/23, 0%), HTLV-1 (0/18, 0%) and syphilis (1/3, 33% reactive, treated latent syphilis). The gene discussed is GSTM1; the disease is latent syphilis.