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Indian Journal of Medical Microbiology, Vol. 28, No. 4, October-December, 2010, pp. 417-418 Correspondence Comparative study of blood culture and Staphylococcal coagglutination test in clinically suspected cases of enteric fever MC Baragundi1, G Vishwanath2, AR Hanumanthappa2, K Suresh2, NR Chandrappa2, CS Patil1 1 Department of Microbiology, S.N. Medical college, Bagalkot- 587101, India Date of Submission: 26-Jun-2010 Code Number: mb10128 PMID: 20966592 DOI: 10.4103/0255-0857.71818 Dear Editor, Enteric fever is endemic in all parts of India. [1] Early and rapid detection of aetiological agent is essential for diagnosis and treatment, to reduce morbidity and mortality.[2] Serological diagnosis is of limited value, and is confusing and difficult to interpret. [3] These tests become positive only from second week onwards. Salmonella antigens in the serum of patients can be demonstrated by sensitised staphylococcal coagglutination test. [1] For the present study, 106 clinically suspected cases of enteric fever were included. Blood culture was done in biphasic Brain Heart Infusion (BHI) bottle, using standard microbiological techniques. Coagglutination test was done with Poly, O9, Hd, Vi coagglutination reagents and controls. [4] O9 and Hd were used together to detect Salmonella typhi specifically because individually they are present in other species also. Vi was used to detect O9 negative (some strains in which O9 is covered by Vi) or Hd negative (non-flagellated) S. typhi. Poly was used to detect all other species of Salmonella together as non-S. typhi, when O9, Hd, or Vi were negative. O2 was not used to detect specifically Salmonella paratyphi A, as its incidence is very low in our locality (based on Widal reports done previously). Out of the 106 cases, blood culture was positive for salmonellae in 19 (17.9%) cases only. Out of them, 17 (89.48%) isolates were S. typhi and 2 (10.52%) were S. paratyphi A. Coagglutination test was positive in 76 (71.6%) cases. All 25 controls were negative by coagglutination and blood culture [Table - 1]. Chi-square test and "Z" test were used for statistical analysis. Isolation of salmonellae from blood culture was low, i.e., 19 (17.9%) cases. Isolation rate decreased with increasing duration of fever. Antibiotic therapy severely affected the isolation of bacilli from blood (P < 0.001). Detection of salmonella antigens by coagglutination test was high, i.e., 76 (71.6%) cases. Rate of detection of antigen by coagglutination test with increasing duration of fever was more, when compared with blood culture, in both antibiotic treated and nontreated patients. Coagglutination results before (83.4%) and after (68.3%) antibiotic therapy were compared and the difference was statistically not significant (P > 0.05), indicating that antibiotic therapy does not affect the results of coagglutination test. [2] Among the 19 blood culture positive cases, coagglutination was positive in 18 (94.7%) cases and negative in 1 case and this can be attributed to the low level of antigenaemia in early phase of illness, [5] as blood was collected on the fifth day of fever in this case. Culture gave positive result as organisms multiplied in culture. Coagglutination was positive in 58 (66.6%) cases in which blood culture was negative. This can be attributed to non-viable or antibiotic-suppressed organisms in the sample, [2] which are detected by coagglutination test but not by blood culture. Poly coagglutination reagent showed positive result in all 76 coagglutination positive tests, O9 was positive in 74 cases. Two cases where O9 was negative showed growth of S. paratyphi A in culture and S. paratyphi A lacks O9 antigen. Hd was positive in 72 cases. Among the four negative results, two were same, which showed S. paratyphi A growth and S. paratyphi A lacks Hd antigen also, and the remaining two can be attributed to non-motile (non-flagellated) variants of S. typhi (confirmed as non-motile variants of S. typhi because O9, Vi were positive and Hd coagglutination was negative). Vi coagglutination showed positive result in 70 cases. Among the six negative results, two were same which showed growth of S. paratyphi A and S. paratyphi A lacks Vi antigen also. Remaining four can be attributed to Vi negative S. typhi. Sensitivity and specificity in the present study were 95 and 100%, respectively. Isolation rate of salmonellae by blood culture is low, especially, if the patient is on antibacterial therapy and if the duration of fever is long. Antigen detection rate by coagglutination test is high even in patients on antibacterial therapy, and the antigens can be detected up to 3 weeks. Coagglutination test is simple, rapid, sensitive, specific, and economical for the detection of Salmonella antigens in the diagnosis of suspected cases of enteric fever, when compared to blood culture. Acknowledgement We thank Dr. Kishore Bhat Head, Department of Microbiology and Molecular Biology, M.M's N. G. Halgekar Institute of Dental Sciences and Research Centre, Belgaum, for his guidance. References
Copyright 2010 - Indian Journal of Medical Microbiology The following images related to this document are available:Photo images[mb10128t1.jpg] |
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