Evaluation of CSF variables as a diagnostic test for bacterial meningitis

Systematic review and validation of diagnostic prediction models in patients suspected of meningitis

OBJECTIVES

Diagnostic prediction models have been developed to assess the likelihood of bacterial meningitis (BM) in patients presented with suspected central nervous system (CNS) infection. External validation in patients suspected of meningitis is essential to determine the diagnostic accuracy of these models.

METHODS

We prospectively included patients who underwent a lumbar puncture for suspected CNS infection. After a systematic review of the literature, we applied identified models for BM to our cohort. We calculated sensitivity, specificity, predictive values, area under the curve (AUC) and, if possible, we evaluated the calibration of the models.

RESULTS

From 2012-2015 we included 363 episodes. In 89 (24%) episodes, the patient received a final diagnosis of a CNS infection, of whom 27 had BM. Seventeen prediction models for BM were identified. Sensitivity of these models ranged from 37% to 100%. Specificity of these models ranged from 44% to 99%. The cerebrospinal fluid model of Oostenbrink reached the highest AUC of 0.95 (95% CI 0.91-0.997). Calibration showed over- or underestimation in all models.

CONCLUSION

None of the existing models performed well enough to recommend as routine use in individual patient management. Future research should focus on differences between diagnostic accuracy of the prediction models and physician's therapeutic decisions.

A ZnO–CNT nanocomposite based electrochemical DNA biosensor for meningitis detection

The article focuses on the synthesis of ZnO and CNTs based electrochemical DNA biosensor and its application towards meningitis DNA detection with high sensitivity as well as selectivity.

Test characteristics and interpretation of cerebrospinal fluid gram stain in children

BACKGROUND

Few data exist regarding the test characteristics of cerebrospinal fluid (CSF) Gram stain among children at risk for bacterial meningitis, especially the rate of false positive Gram stain.

METHODS

We conducted a retrospective cohort study of children seen in the emergency department of Children's Hospital Boston who had CSF obtained between December 1992 and September 2005. Patients who had ventricular shunts, as well as those who received antibiotics before CSF was obtained were excluded. Test characteristics of CSF Gram stain were assessed using CSF culture as the criterion standard. Patients were considered to have bacterial meningitis if there was either: (1) growth of a pathogen, or (2) growth of a possible pathogen noted on the final CSF culture report and the patient was treated with a course of parenteral antibiotics for 7 days or more without other indication.

RESULTS

A total of 17,569 eligible CSF specimens were collected among 16,036 patients during the 13-year study period. The median age of study subjects was 74 days. Seventy CSF specimens (0.4%) had organisms detected on Gram stain. The overall sensitivity of Gram stain to detect bacterial meningitis was 67% [42 of 63; 95% confidence interval (CI): 54-78] with a positive predictive value of 60% (42 of 70; 95% CI: 48-71). Most patients without bacterial meningitis have negative Gram stain [specificity 99.9% (17,478 of 17,506; 95% CI: 99.8-99.9)] with a negative predictive value of 99.9 (17,478 of 17,499; 95% CI: 99.8-99.9).

CONCLUSIONS

CSF Gram stain is appropriately used by physicians in risk stratification for the diagnosis and empiric treatment of bacterial meningitis in children. Although a positive Gram stain result greatly increases the likelihood of bacterial meningitis; the result may be because of contamination or misinterpretation in 40% of cases and should not, by itself, result in a full treatment course for bacterial meningitis.

Bacterial meningitis in children: critical care needs

Acute bacterial meningitis (ABM) in children is associated with a high rate of acute complications and mortality, particularly in the developing countries. Most of the deaths occur during first 48 hours of hospitalization. Coma, raised intracranial pressure (ICP), seizures, shock have been identified as significant predictors of death and morbidity. This article reviews issues in critical care with reference to our experience of managing 88 children with ABM in PICU. Attention should first be directed toward basic ABCs of life-support. Children with Glasgow Coma Scale (GSC) score < 8 need intubation and supplemental oxygen. Antibiotics should be started, even without LP (contraindicated if focal neuro-deficit, papilledema, or signs of raised ICP). Raised ICP is present in most of patients; GCS < 8 and high blood pressure are good guides. Mannitol (0.25 gm/Kg) should be used in such patients. If there are signs of (impending) herniation short-term hyperventilation is recommended; prolonged hyperventilation (> 1 hour) must be avoided. Any evidence of poor perfusion, hypovolemia and/or hypotension needs aggressive treatment with normal saline boluses and inotropes, if necessary, to maintain normal blood pressure. Empiric fluid restriction is not justified. Seizures may be controlled with intravenous diazepam or lorazepam. Refractory status epilepticus may be treated with continuous diazepam (0.01-0.06) mg/kg/min) or midazolam infusion. Ventilatory support may be needed early for associated pneumonia, poor respiratory effort and/or coma, and occasionally to reduce work of breathing in shock. Provision of critical care to children with ABM may reduce the mortality significantly as experienced by us.

Quality assurance study of bacterial antigen testing of cerebrospinal fluid

Bacterial antigen testing (BAT) of cerebrospinal fluid (CSF) by latex agglutination is a low-yield procedure in patients whose CSF specimens have normal laboratory parameters. Between August 1992 and August 1994, we evaluated 287 bacterial antigen (BA) test requests to determine whether yields could be improved and whether patient costs could be reduced by cancelling BAT for those patients with normal CSF parameters (cell count, protein, glucose) after consultation with physicians. A total of 171 (68%) BA tests were canceled by this approach. None of these CSF specimens was culture positive for an organism detectable by BAT. Of the remaining 116 CSF specimens tested, only 3 were positive by BAT, one each for Neisseria meningitidis, Streptococcus pneumoniae, and group B streptococcus. Only 43 of the CSF specimens tested had at least two abnormal parameters; the 3 positive CSF specimens were included in this group. In light of the low rate of positivity, the number of BA tests can be further reduced by establishing criteria that must be met before a CSF specimen is accepted for BAT. After review of our data and the literature concerning this topic, we concluded that only specimens with leukocyte counts of > or = 50 cells per mm3 should be tested. Of 287 specimens evaluated in our study, only 36 met this criterion, including the 3 BA-positive specimens. Enacting such a restriction would have reduced the total number of BA tests by 251 (87%) without compromising patient care. A laboratory cost savings of $6,500 per year would have been realized, with a substantial reduction in the cost per positive test. Patient charges would have been reduced by $12,500 per year.