Detection of chloramphenicol resistance in Haemophilus influenzae.

An average of 358 (13%) of United Kingdom laboratories failed to detect resistance to chloramphenicol in strains of Haemophilus influenzae distributed by the United Kingdom National External Quality Assessment Scheme for Microbiology. Clear associations between methods used and results obtained show that error rates are minimised by the use of low content (10 micrograms) disc and a sensitive control strain of H influenzae.