Sepsis is a serious medical condition requiring timely administered, appropriate antibiotic therapy. Blood culture is regarded as the gold standard for aetiological diagnosis of sepsis, but it suffers from low sensitivity and long turnaround time. Thus, nucleic acid amplification tests (NAATs) have emerged to shorten the time to identification of causative microbes. The aim of the present study was to evaluate the clinical utility in everyday practice in the emergency department of two commercial NAATs in patients suspected with sepsis.
During a six-week period, blood samples were collected consecutively from all adult patients admitted to the general emergency department for suspicion of a community-onset sepsis and treated with intravenous antibiotics. Along with conventional blood cultures, multiplex PCR (Magicplex™) was performed on whole blood specimens whereas portions from blood culture bottles were used for analysis by microarray-based assay (Prove-it™). The aetiological significance of identified organisms was determined by two infectious disease physicians based on clinical presentation and expected pathogenicity.
Among 382 episodes of suspected sepsis, clinically relevant microbes were detected by blood culture in 42 episodes (11%), by multiplex PCR in 37 episodes (9.7%), and by microarray in 32 episodes (8.4%). Although moderate agreement with blood culture (kappa 0.50), the multiplex PCR added diagnostic value by timely detection of 15 clinically relevant findings in blood culture-negative specimens. Results of the microarray corresponded very well to those of blood culture (kappa 0.90), but were available just marginally prior to blood culture results.
The use of NAATs on whole blood specimens in adjunct to current culture-based methods provides a clinical add-on value by allowing for detection of organisms missed by blood culture. However, the aetiological significance of findings detected by NAATs should be interpreted with caution as the high analytical sensitivity may add findings that do not necessarily corroborate with the clinical diagnosis.
Department of Clinical Microbiology, Institute of Regional Health Services Research, University of Southern Denmark, Lillebaelt Hospital, Kabbeltoft 25, DK-7100 Vejle, Denmark. jkm@dadlnet.dk
To evaluate a routine notification of general practitioners to recall nucleic acid amplification test (NAAT)-positive subjects for culture of Neisseria gonorrhoeae to confirm gonococcal infection in the community.
A retrospective observational study of the routine testing for N gonorrhoeae by analysis of test results compiled from the laboratory information system in two departments of clinical microbiology.
Altogether, 158 male and female subjects with NAAT-positive results for N gonorrhoeae were included in the study. Samples for culture of N gonorrhoeae were collected from 102/158 (64.6%) subjects recalled after a NAAT assay was found positive. Growth of N gonorrhoeae was seen in the samples from 54/102 (52.9%) of the re-examined NAAT-positive subjects. Among subjects with samples collected within the first week after the positive NAAT test, 34/44 (77.3%) were confirmed positive by culture.
This study shows that it is possible for the general practitioner to recall a substantial number of NAAT-positive subjects to collect swabs for culture of N gonorrhoeae to confirm gonococcal infection in the community. Most recall samples are culture positive if collected within a week of the NAAT-positive test, and may provide a sufficient monitoring of the drug susceptibility of N gonorrhoeae strains in the community.
Detection of hepatitis C virus and human immunodeficiency virus-1 antibody-negative donations: Canadian Blood Services' experience with nucleic acid testing.
Provincial Laboratory for Public Health (Microbiology), and Department of Microbiology and Infectious Diseases, University of Calgary, Calgary, Alberta, Canada. p.tilley@provlab.ab.ca
Although nucleic acid amplification testing (NAAT) for West Nile virus (WNV) is useful in screening blood donors, such methods have not been studied in symptomatic patients. For diagnosis of WNV infection, 1.0 mL of plasma was tested by NAAT, and WNV-specific immunoglobulin M was assayed. Of 276 WNV cases, 191 were tested by both serology and NAAT. Of these, 86 (45.0%), 111 (58.1%), and 180 (94.2%) were detected by NAAT, serology, and combined NAAT and serology, respectively. NAAT-based screening was most useful within 8 days of the onset of symptoms. Viremia is common in early symptomatic WNV infection, and NAAT enhances diagnostic yield.
