Prevalence of Fusobacterium necrophorum and other upper respiratory tract pathogens isolated from throat swabs

Fusobacterium necrophorum, an anaerobic, Gram-negative rod, has been identified recently as a significant cause of persistent sore throat syndrome (PSTS). This disease is characterised by chronic, recurrent or persistent sore throat, which is believed to respond poorly to penicillin in vivo. The aim of this study is to examine the prevalence of F necrophorum in all throat swabs received in our diagnostic microbiology department and to compare the results with those for other recognised respiratory pathogens. All throat swabs received in the laboratory over a four-week period were cultured for beta-haemolytic streptococcus groups A, C and G, Corynebacterium diphtheriae, Arcanobacterium haemolyticum and F necrophorum. Latex agglutination techniques, phenotypic reactions and antibiograms are used to identify these organisms. The age of the patient and the clinical details as stated on the request form were noted. Among a total of 248 samples, 27 were positive for P-haemolytic streptococcus group A, two were positive for beta-haemolytic streptococcus group C, five were positive for beta-haemolytic streptococcus group G and 24 were positive for F necrophorum. The most common isolate in the under 20 age group was beta-haemolytic streptococcus group A. In the over 20 age group, F necrophorum was the pathogen most frequently isolated. A clinical diagnosis of 'sore throat' was most likely to be positive for beta-haemolytic streptococcus group A, a clinical diagnosis of PSTS was most likely to be positive for F necrophorum and a clinical diagnosis of 'tonsillitis' was equally likely to be caused by beta-haemolytic streptococcus group A or F necrophorum. beta-haemolytic streptococcus group A was present in 11% of the samples and F necrophorum was present in 10% of the samples. In total, these two pathogens accounted for 18.5% of throat infections in the sampled group. The results show that F necrophorum is as significant a cause of throat infection as is beta-haemolytic streptococcus group A. Examination of this provisional data suggests that targeting culture towards these two pathogens may be possible in certain cohorts of patients if more precise clinical data are received from medical staff. However, based on the clinical symptoms routinely provided by clinicians requesting microscopy, culture and sensitivity on throat swabs, F necrophorum culture is required on all throat swabs received in the laboratory.