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Year : 2005  |  Volume : 23  |  Issue : 4  |  Page : 270--271

Incubation period for culture positivity to detect septicaemia in neonates

CS Vinod Kumar, YF Neelagaud 
 Department of PG Studies and Research in Microbiology, Gulbarga University, Gulbarga 585 106, Karnataka, India

Correspondence Address:
C S Vinod Kumar
Department of PG Studies and Research in Microbiology, Gulbarga University, Gulbarga 585 106, Karnataka

How to cite this article:
Vinod Kumar C S, Neelagaud Y F. Incubation period for culture positivity to detect septicaemia in neonates.Indian J Med Microbiol 2005;23:270-271

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Vinod Kumar C S, Neelagaud Y F. Incubation period for culture positivity to detect septicaemia in neonates. Indian J Med Microbiol [serial online] 2005 [cited 2020 Dec 3 ];23:270-271
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Dear Editor,

Neonatal septicaemia, its high incidence and its grave prognosis, in spite of all modern antibiotics, have been a challenge for all times. The clinical signs of neonatal sepsis are subtle and nonspecific and often the diagnosis is difficult to establish on the basis of clinical findings alone.[1] Hence, the laboratory has a very significant role to play in the diagnosis of neonatal septicemia. Of all newborns, 3 to 5 per 1000 of newborns admitted to a newborn intensive care unit have culture-proven septicaemia.[1],[2] Some investigators believe that these figures may underestimate the true bloodstream infection rate and that many cases remain undocumented.[2] Because of this assumption, the length of treatment is often based as much on the physician's clinical assessment of the infant's status as on the microbiologic results. Sick newborns may be treated with antibiotics for 5 to 10 days if such therapy is warranted by clinical assessment,[2] even if blood cultures remain negative. Some asymptomatic newborns are started on antibiotics because of maternal risk factors. Others receive antibiotics for minor symptoms that resolve quickly. Patients in these groups are often treated until it is clear that blood cultures are not positive. A critical issue for these and other infants is the time at which one can assume that blood cultures negative to date will not subsequently become positive.

The literature has not resolved the question of when a blood culture can safely be considered negative. Many laboratories continue to observe culture media for 7 to 10 days. Yet many nurseries discontinue antibiotic therapy after seven days. These unsettled questions for both clinician and the laboratory were the subject of our study. How many septic newborns would be inadequately treated if therapy was stopped at four days, how many newborns would be treated unnecessarily and have their hospital stay prolonged if a longer period of blood culture incubation were adopted and what is the optimal time for the laboratory to continue monitoring sample?

Blood samples from 1647 suspected neonatal septicaemic cases were cultured over a period of four years. Organisms were identified by conventional methods.[3],[4] Table shows day on which organisms were recovered from blood cultures obtained from neonates. Of the 1647 samples cultured, 877 were positive by the end of seven days processing period yielding 781 bacterial isolates and 96 yeasts. Five (0.5%) organisms were recovered on the day the culture was submitted (day 0), and 383 (43.7%) of positive cultures were identified by day 1.

Out of 877, 781(89.1%) isolates were detected as positive by day 2, 858 (97.8%) were detected as positive by day 3, and 873 (99.5%) were detected as positive by day 4.The predictive value of blood cultures that were negative at day 4 was clinically similar to that of waiting for 7 days of processing before discontinuing therapy. No septic infants were missed in the study, since growth is not the only parameter taken into account for the treatment of newborns. If one chose to continue therapy until blood cultures were negative for 7 days of processing, then the neonates already having been treated for antibiotics for four days, would have been treated and hospitalized for three extra days each to detect four organisms. Discontinuation of intravenous lines and antibiotic therapy and early discharge would decrease the risk of iatrogenic complications and nosocomial infections. From this study we conclude, that four days processing period will detect positive blood culture of virtually all important infections and clinical benefit from continuing blood culture processing beyond four days does not justify the time and cost involved.


1Chugh K, Aggarwal BB, Kaul VK, Arya SC. Bacteriological profile of neonatal septicemia. Indian J Pediatrics 1988; 55 :961-5.
2Gerdes JS, Polin. Early diagnosis and treatment of neonatal sepsis. Indian J Pediatr 1998; 65: 63-78.
3Parikh M, Singh N. Rapid diagnosis of neonatal bacteraemia. Indian J Med Microbiol 1995; 13 :37-40
4Kumar S, Rizvi M, Vidhani S. Changing face of septicaemia and increasing drug resistance in blood isolates. Indian J Patho Microbiol 2004; 47 :441-5.