Efficiency of cultures of rectal swabs and faecal specimens in detecting salmonella carriers: correlation with numbers of salmonellas excreted

Abstract

The comparative efficiency of cultures of rectal swabs and faecal specimens in detecting salmonellas in asymptomatic carriers was determined and then correlated with the number of salmonellas excreted per g. of faeces (wet weight). In six short-term salmonella carriers, 82% of rectal swab cultures taken daily for 11 consecutive days were positive for salmonellas, whereas 94% of faecal specimens cultured were positive. Similarily, in 8 long-term carriers, 58% of the rectal swab cultures were positive as compared with 91% of faecal specimens. The inferiority of the results of rectal swab cultures correlated with their inefficiency in detecting salmonellas when fewer than 1000 salmonellas per g. of faeces were present.The patterns of salmonella excretion as depicted by estimated salmonella content of faecal specimens showed that all carriers had irregular day-to-day variations. The average number of salmonellas excreted per g. of faeces by short-term carriers was greater than that by long-term carriers, although both groups revealed the same wide variations in number of organisms excreted.The effect of delayed processing and shipment of specimens upon recovery of salmonellas was also studied. No deleterious effects were noted when specimens were shipped and processing was delayed for up to 3 days.