Diagnosis

In a patient with suspected meningococcal disease, diagnosis can be made by using microbiological culture of blood, cerebrospinal fluid, or aspirates from the hemorrhagic rash. Sensitivities of approximately 30% have been reported for diagnosis by blood culture.[4] These low levels of diagnostic sensitivity may be related to collection of blood and cerebrospinal fluid (CSF) after the first dose of antibiotics has been administered, as meningococci are rapidly killed following a single dose of intravenous penicillin. In the United Kingdom and some countries in Europe, antibiotics are given in primary care to reduce the potential for deterioration of the patient's condition during transport to the hospital.

Recently, diagnostic sensitivity has been improved by the introduction of polymerase chain reaction (PCR)-based molecular diagnostic methods into clinical practice. Blood or CSF can be taken from a suspected clinical case and meningococcal infection can be confirmed by identification of meningococcal gene sequences, which can persist in these fluids up to 4 days after the start of antibiotic treatment. Whereas molecular characterization utilizes genes with significant variation to distinguish different clones, clinical diagnosis requires the identification of genes conserved across all meningococci. In the United Kingdom, sensitive and specific assays have been developed using the ctrA gene, encoding a protein involved in capsular synthesis and transport.[2] This gene is specific to N. meningitidis, and common to all menin-gococcal serogroups. During recent clinical evaluation of

95 children with probable meningococcal disease, 82 (88%) had a positive PCR, whereas 32 (33%) were culture-positive.[3] No false negative PCR results were obtained with this protocol because all culture positive cases were confirmed by PCR. False negatives were observed in a previous ctrA PCR assay using different oligonucleotide PCR primers on serum or plasma samples.1-4-1 Whereas false positive results have been observed in an assay based on the IS1106 insertion sequence,1-5-1 which may be found in other microorganisms, no false positives have been observed to date with the ctrA PCR assay.

A further advance has been the development of a single-tube multiplex, real-time PCR assay for detection of all the organisms forming the major differential diagnosis of significant childhood sepsis and meningitis in Europe and North America.1-6-1 This uses fluorescent dye-labeled sequence-specific probes for the simultaneous detection of the N. meningitidis capsular transport gene (ctrA), Haemophilus influenzae capsulation gene (bexA), and Streptococcus pneumoniae pneumolysin gene (ply). As soon as meningococcal infection is confirmed, the serogroup of the infecting organism can be determined. A PCR-based assay is used to detect the siaD gene, which encodes the serogroup-specific sialyltransferase enzyme, enabling differentiation of serogroup B, C, Y, and W135 organisms.1-7,8-1 This assay is less sensitive in terms of detection of meningococci than the ctrA PCR assay. Serogroup A bacteria can be identified by PCR detection of the mynA gene, which encodes an enzyme involved in synthesis of the serogroup A capsular polysaccharide.1-9-1

Getting Started With Dumbbells

Getting Started With Dumbbells

The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.

Get My Free Ebook


Post a comment