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.     

Haemophilus influenzae type b still remains a leading cause of meningitis among unvaccinated children--a prospective CSF analysis study

A prospective, hospital-based cerebrospinal fluid (CSF) analysis study was undertaken in 65 children who had diagnostic lumbar puncture on admission for suspected central nervous system infections. Twenty-three children were clinically diagnosed to have had sepsis and/or meningitis. CSF bacterial culture grew Haemophilus influenzae type b (Hib) in four cases and Streptococcus pneumonia (SP) was cultured in another child. Bacterial antigen was detected in 13 other CSF specimens and the pathogens were Hib (n = 9), SP (n = 3) and Group B Streptococcus (n = 1). No etiologic cause was identified to explain the abnormal CSF pleocytosis and biochemistry in the remaining five cases. In contrast, the CSF analysis was normal in 42 other children with probable viral and non-infectious neurological condition, mostly febrile convulsions. The overall frequency rate for all types of meningitis and especially for Hib meningitis were 43 and 31 cases per 100,000 children < 5 years of age, respectively. These findings support our earlier observations that Hib meningitis still remains the leading cause of childhood meningitis in our region. Also it reaffirms the observation that bacterial meningitis may often be under-reported if CSF positive culture alone is considered for the diagnosis.     

Evaluation of polymerase chain reaction (PCR) for diagnosing Haemophilus influenzae b meningitis

A polymerase chain reaction (PCR) for detecting Hib in cerebrospinal fluid (CSF) was evaluated and compared with culture and a latex agglutination test (LAT) in a hospital-based prospective surveillance. We studied 107 children aged from 1 month to 12 years with a clinical and CSF profile suggestive of acute bacterial meningitis. CSF culture was performed on blood-chocolate agar by standard technique, LAT by a commercially available kit (Wellcogen) and PCR using total DNA extracted from CSF samples. Of 107 children, 79% had received one or more doses of injectable antibiotics. Hib was detected by culture in 14 cases, by LAT in 23 and by PCR in 37. All CSF samples that reveal Hib by culture or LAT had a PCR positive for Hib (sensitivity 100%). PCR also detected 14 additional cases of Hib meningitis which were not detected by culture or LAT. We conclude that PCR is a sensitive and specific diagnostic tool that may be valuable in a population with high pre-hospital antibiotic usage.     

Clinically inapparent meningitis complicating periorbital cellulitis

Two young children with periorbital (preseptal) cellulitis were found to have meningitis despite having no signs of meningeal irritation and normal cerebrospinal fluid (CSF) cell counts and chemistries. These cases are reported to remind physicians caring for acutely ill children that periorbital cellulitis can have life-threatening complications and that meningitis can occur in the absence of significant clinical signs and in the presence of an initially normal CSF.     

A clear CSF is not always a normal CSF

A normal initial cerebrospinal fluid (CSF) study has been traditionally used to exclude the potential diagnosis of bacterial meningitis. However, cases of pyogenic meningitis in the absence of CSF pleocytosis have been reported in which smears for gram stain or CSF culture revealed the diagnosis of meningitis. In the presence of clinical signs of meningitis, an abnormal initial CSF study indicates a diagnosis of bacterial meningitis but a normal result may not necessarily exclude it and therefore, should not delay early institution of appropriate antimicrobial therapy.     

C-reactive protein is useful in distinguishing Gram stain-negative bacterial meningitis from viral meningitis in children.

OBJECTIVE: To clarify to what extent Gram stain-negative bacterial meningitis can be distinguished from viral meningitis by assessment of cerebrospinal fluid (CSF) and blood indices and serum C-reactive protein (CRP) in children over 3 months of age. DESIGN: Common CSF indices, blood leukocyte counts, and serum CRP values were compared between patients with bacterial meningitis who had a positive CSF bacterial culture but a negative Gram stain and patients with viral meningitis. POPULATION: Three hundred twenty-five consecutive patients with CSF culture-proven bacterial meningitis, for whom Gram stain was negative in 55 cases, and 182 children with proven or presumed viral meningitis. RESULTS: Significant differences between patients with bacterial and viral meningitis were found in all indices with large overlap in all except serum CRP. In patients with bacterial meningitis, the mean CSF glucose concentration, protein concentration, leukocyte count, blood leukocyte count, and serum CRP were 2.9 mmol/L (52 mg/dL), 1.88 g/L, 4540 x 10(6)/L, 18.0 x 10(9)/L, and 115 mg/L; and in those with viral meningitis, mean values were 3.3 mmol/L (59 mg/dL), 0.52 g/L, 240 x 10(6)/L, 10.6 x 10(9)/L, and <20 mg/L, respectively. Of the tests investigated in this study, only serum CRP was capable of distinguishing Gram stain-negative bacterial meningitis from viral meningitis on admission with high sensitivity (96%), high specificity (93%), and high negative predictive value (99%). CONCLUSION: Exclusion of bacterial meningitis with only the conventional tests is difficult. Combined with careful physical examination and CSF analyses, serum CRP measurement affords substantial aid.     

A diagnostic rule for tuberculous meningitis.

Diagnostic confusion often exists between tuberculous meningitis and other meningoencephalitides. Newer diagnostic tests are unlikely to be available in many countries for some time. This study examines which clinical features and simple laboratory tests can differentiate tuberculous meningitis from other infections. Two hundred and thirty two children (110 tuberculous meningitis, 94 non-tuberculous meningitis, 28 indeterminate) with suspected meningitis and cerebrospinal fluid (CSF) pleocytosis were enrolled. Tuberculous meningitis was defined as positive CSF mycobacterial culture or acid fast bacilli stain, or basal enhancement or tuberculoma on computed tomography (CT) scan with clinical response to antituberculous treatment. Non-tuberculous meningitis was defined as positive CSF bacterial culture or Gram stain, or clinical response without antituberculous treatment. Thirty clinical/laboratory features of patients with tuberculous meningitis and non-tuberculous meningitis were compared by univariate and multiple logistic regression analysis. Five features were independently predictive of the diagnosis of tuberculous meningitis (p < 0.007): prodromal stage >/= 7 days, optic atrophy on fundal examination, focal deficit, abnormal movements, and CSF leucocytes < 50% polymorphs. When validated on another set of 128 patients, if at least one feature was present, sensitivity was 98.4% and, if three or more were present, specificity was 98.3%. This simple rule would be useful to physicians working in regions where tuberculosis is prevalent.     

Rapid sterilisation of cerebrospinal fluid in meningococcal meningitis: Implications for treatment duration

AIM: The aim of this study was to determine the time and total cumulative dose of parenteral antibiotic, required to sterilize the cerebrospinal fluid (CSF) of children presenting with meningococcal meningitis (MM). METHODS: The study was a retrospective audit of children aged 0-14 years who presented between January 1995 and December 1999 with MM. All cases had a delayed lumbar puncture (LP) at least 1 h after commencing antibiotic therapy and demonstrated at least one of the following: (i) a positive CSF culture of Neisseria meningitidis (n = 6); (ii) Gram negative diplococci on Gram stain (n = 16) or (iii) a positive CSF plasma clearance rate test for N. meningitidis (n = 26). RESULTS: Forty-eight children were identified with a mean age of 4.4 years. The cumulative dose of antibiotic prior to LP, ranged from 22 to 440 mg/kg body weight. All cases (n = 24) who received a cumulative dose of at least 150 mg/kg of antibiotic, prior to LP, had a sterile CSF. No CSF taken more than 5 h after commencing antibiotics grew N. meningitidis. CONCLUSIONS: Children in this study with MM had rapid sterilisation of the CSF in less than 6 h. This would support recent recommendations to reduce the duration of antibiotic therapy to 4 days. There is however, lack of long-term data on sequelae with 4 days of treatment.     

Bacterial antigen detection test in meningitis

Objective : To evaluate the role of bacterial antigen detection test in cerebrospinal fluid (CSF) for a rapid etiological diagnosis of bacterial meningitis.Methods : The study included 36 cases of bacterial meningitis and 14 controls. Latex particle agglutination test (LPA test) for detection of bacterial antigen was done in the CSF using slidex meningitis kit (Biomeriux, France).Results : Using LPA test, an etiological diagnosis could be made in 83% cases of bacterial meningitis. In contrast, CSF Gram stain and culture showed 36% and 6% positivity, respectively. The sensitivity and specificity of LPA test were 83% and 100%, respectively. The common etiological organisms were S.pneumoniae, H. influenzae type b andN. meningitidis A. S. pneumoniae was encountered in all age groups whileH. influenzae type b was found only below one year of age.Conclusions : LPA test is a rapid and superior diagnostic tool as compared to CSF Gram stain and culture. The study recommends LPA test as an adjunct laboratory test for rapid etioiogical diagnosis of bacterial meningitis for prompt institution of proper antibiotics.     

Impact of haemophilus influenzae type b conjugate vaccine in South Africa and Argentina

INTRODUCTION: Haemophilus influenzae type b (Hib) persists as a major cause of pediatric meningitis and pneumonia in developing countries in which Hib conjugate vaccines are not used. Demonstration of decreases in severe Hib disease after countries introduce Hib conjugate vaccine will help justify the resources necessary to purchase and provide the vaccine. Because surveillance for culture-confirmed Hib meningitis is not available in many countries, alternative means to measure the impact of Hib conjugate vaccine would be useful. METHODS: Laboratory records from the years before and after introduction of the Hib conjugate vaccine were reviewed at 4 hospitals, 2 in Argentina and 2 in South Africa. Potential indicators of bacterial meningitis including cerebrospinal fluid (CSF) culture, white blood cell count, appearance, protein and glucose were recorded. RESULTS: After introduction of Hib conjugate vaccine, culture-confirmed Hib meningitis declined significantly at 3 of 4 hospitals (2 in Argentina and 1 in South Africa). In the same 3 hospitals, there was a significant decline after vaccine introduction in some of the following CSF indicators of bacterial meningitis: proportion of CSF specimens with white blood cell count > or = 100 x 10(6)/L, 500 x 10(6)/L and 1,000 x 10(6)/L; glucose <40 mg/dL; protein >100 mg/dL; and turbid appearance. CONCLUSIONS: Culture-confirmed Hib meningitis declined at 3 of the 4 hospitals after Hib vaccine introduction. Surrogate indicators of bacterial meningitis also declined and might be useful measures of Hib conjugate vaccine impact at hospitals where capacity to culture Hib is not available.     

Effect of prior antibiotic therapy on concentrations of bacteria in CSF.

A prospective study was done to determine the effect of prior antibiotic therapy on concentrations of bacteria in CSF at the time of diagnosis. Concentrations of Haemophilus influenzae type b in CSF of partially treated patients were significantly smaller than in CSF of untreated patients. This was also true of patients with meningococcal meningitis, but no difference was observed between patients with pneumococcal meningitis. The identification of H influenzae by Gram stain of CSF was significantly decreased by prior antibiotic therapy. Measurable levels of antibiotic (penicillins, aminoglycosides) were present in CSF of ten of 23 patients. Two partially treated patients were diagnosed by detection of meningococcal antigen in CSF by counterimmunoelectrophoresis although cultures of CSF were sterile. Both of these patients had measurable levels of penicillin in CSF. These data indicate that prior antibiotic therapy significantly decreases the concentration of H influenzae type b and meningococcus in CSF and therefore decreases the usefulness of CSF Gram stain. Partial therapy may sterilize the CSF of some patients.     

Assessment of a commonly available latex particle agglutination test in rapid, bacteriologic cerebrospinal fluid diagnosis

36 cerebrospinal fluid specimens (CSF) from patients with bacterial meningitis were tested for the presence of bacterial antigens with the "Slidex Meningite Kit" (Bio Merieux). This kit has latex particles coated with antibodies against hemophilus influenzae type B (Hib) streptococcus pneumoniae (SP) and neisseria meningitidis (NM) group A and C. With the LAT we could detect the bacterial antigens in 84% of bacterial meningitis cases, 23 of the 27 of Hib meningitis (85.2%), all of the 6 cases of SP meningitis (100%) and two of the three NM meningitis cases. The test is handicapped by the fact, that there is no antiserum against NM sero-group B, the main cause of NM meningitis in Austria. There were no false positive results with the LAT. False negative results were obtained in 19.2% of Hib and in one case of NM. Even under sufficient antibiotic therapy and with negative culture we could detect 9 Hib- and 1 NM-cases during the first 12-48 hours of therapy with this method. The LAT-Kit is a useful addition to standard methods of CSF examinations in bacterial meningitis. With the LAT a rapid bacteriological diagnosis is possible within 15 minutes. The Kit is also able to identify bacterial antigens even with negative culture and after initiation of antibiotic treatment.     

Invasive Haemophilus influenzae type B diseases in Bangladesh, with increased resistance to antibiotics

OBJECTIVE: To determine the prevalence, age-group distribution, serotype, and antibiotic susceptibility patterns of invasive Haemophilus influenzae type b (Hib) isolates in Bangladeshi children because data regarding Hib diseases in developing countries are scarce, which has led to delay of the introduction of Hib vaccine in these countries. METHODS: Children diagnosed with meningitis (n = 1412) and pneumonia (n = 2434) were enrolled in this surveillance study for Hib invasive diseases. Cerebrospinal fluid (CSF) and blood specimens, and the subsequent isolates, were processed using standard procedures. RESULTS: During 1993 to 2003, 455 H influenzae strains were isolated from patients with meningitis (n = 425) and pneumonia (n = 30), and an additional 68 Hib meningitis cases were detected by latex agglutination (LA) testing. Overall, 35% of pyogenic meningitis cases were a result of H influenzae, 97.1% of which were Hib. Most (91.4%) cases occurred during the first year of life. Resistance to ampicillin, chloramphenicol, and cotrimoxazole was 32.5%, 21.5%, and 49.2%, respectively. There was a trend toward increasing resistance for all three drugs. Resistance to ampicillin and chloramphenicol was almost universally coexistent and was associated with increased sequelae compared with the patients infected with susceptible strains (31% [23/75] vs 11% [21/183]; P <.001). CONCLUSION: Hib is the most predominant cause of meningitis in young Bangladeshi children. Resistance to ampicillin and chloramphenicol and the high cost of third-generation cephalosporin highlight the importance of disease prevention through vaccination against Hib.     

Cerebrospinal fluid enrichment broth cultures rarely contribute to the diagnosis of bacterial meningitis

This study included children undergoing lumbar puncture in the emergency department. Bacteria were isolated from 34 (1.7%) of 1898 cerebrospinal fluid (CSF) enrichment broth cultures; 30 were contaminants. The primary CSF Gram stain was negative in all specimens with a positive enrichment broth culture. Enrichment broth cultures rarely contributed to the diagnosis of bacterial meningitis, and positive CSF enrichment broth cultures contributed to diagnostic uncertainty.     

Clinical decision rules to distinguish between bacterial and aseptic meningitis.

BACKGROUND: Clinical decision rules have been derived to distinguish between bacterial and aseptic meningitis in the emergency room to avoid unnecessary antibiotic treatments and hospitalisations. AIMS: To evaluate the reproducibility and to compare the diagnostic performance of five clinical decision rules. METHODS: All children hospitalised for bacterial meningitis between 1995 and 2004 or aseptic meningitis between 2000 and 2004 have been included in a retrospective cohort study. Sensitivity and specificity were calculated by applying each rule to the patients. The best rule was a priori defined as the one yielding 100% sensitivity for bacterial meningitis, the highest specificity, and the greatest simplicity for a bedside application. RESULTS: Among the 166 patients included, 20 had bacterial meningitis and 146 had aseptic meningitis. Although three rules achieved 100% sensitivity (95% CI 84-100), one had a significantly lower specificity (13%, 95% CI 8-19) than those of the other two rules (57%, 95% CI 48-65; and 66%, 95% CI 57-73), which were not statistically different. The ease of manual computation of the rule developed by Nigrovic et al (a simple list of five items: seizure, blood neutrophil count, cerebrospinal fluid (CSF) Gram stain, CSF protein, CSF neutrophil count) was higher than the one developed by Bonsu and Harper. CONCLUSION: On our population, the rule derived by Nigrovic et al had the best balance between accuracy and simplicity of manual computation and could help to avoid two thirds of unnecessary antibiotic treatments and hospitalisations.     

The emergence of resistant pneumococcal meningitis--implications for empiric therapy

Background: Following the emergence of penicillin and cephalosporin resistant pneumococcal meningitis in the United States, inclusion of vancomycin in empiric therapy for all suspected bacterial meningitis was recommended by the American Academy of Pediatrics. Few data are available to evaluate this policy. Aims: To examine the management and clinical course in relation to antibiotic therapy of a large unselected cohort of children with pneumococcal meningitis in a geographic area where antibiotic resistance has recently increased. Methods: Retrospective review of all cases of pneumococcal meningitis in a defined population (Sydney, Australia), 1994–99. Results: A total of 104 cases without predisposing illnesses were identified; timing of lumbar puncture (LP) was known in 103. Resistance to penicillin increased from 0 to 20% over the study period. Only 57 (55%) had an early LP (prior to parenteral antibiotics); 55 (96%) had organisms on Gram stain. Severe disease (intensive care admission or death) increased significantly from 57 cases with early LP (28%) to 33 with delayed LP (42%) to 13 with no LP (62%). Evidence of pneumococcal infection was available within 24 hours in 85% of those with delayed or no LP. Outcome was not related to empiric vancomycin use, which increased from 5% prior to 1998 to 48% in 1999. Conclusion: LP is frequently delayed in pneumococcal meningitis. Based on disease severity, empiric vancomycin is most justified when LP is deferred. If an early LP is done, vancomycin can be withheld if Gram positive diplococci are not seen.     

The emergence of resistant pneumococcal meningitis--implications for empiric therapy.

BACKGROUND: Following the emergence of penicillin and cephalosporin resistant pneumococcal meningitis in the United States, inclusion of vancomycin in empiric therapy for all suspected bacterial meningitis was recommended by the American Academy of Pediatrics. Few data are available to evaluate this policy. AIMS: To examine the management and clinical course in relation to antibiotic therapy of a large unselected cohort of children with pneumococcal meningitis in a geographic area where antibiotic resistance has recently increased. METHODS: Retrospective review of all cases of pneumococcal meningitis in a defined population (Sydney, Australia), 1994-99. RESULTS: A total of 104 cases without predisposing illnesses were identified; timing of lumbar puncture (LP) was known in 103. Resistance to penicillin increased from 0 to 20% over the study period. Only 57 (55%) had an early LP (prior to parenteral antibiotics); 55 (96%) had organisms on Gram stain. Severe disease (intensive care admission or death) increased significantly from 57 cases with early LP (28%) to 33 with delayed LP (42%) to 13 with no LP (62%). Evidence of pneumococcal infection was available within 24 hours in 85% of those with delayed or no LP. Outcome was not related to empiric vancomycin use, which increased from 5% prior to 1998 to 48% in 1999. CONCLUSION: LP is frequently delayed in pneumococcal meningitis. Based on disease severity, empiric vancomycin is most justified when LP is deferred. If an early LP is done, vancomycin can be withheld if Gram positive diplococci are not seen.     

Acute bacterial meningitis. Cerebrospinal fluid differential count

A retrospective analysis of 112 cases of pediatric bacterial meningitis over a 3-year period was performed to determine the rate of cerebrospinal fluid (CSF) lymphocytosis at initial evaluation. Of 14 neonates and 98 children older than 1 month of age not receiving preadmission antibiotic therapy, only one instance of CSF lymphocytosis occurred. This patient's CSF exhibited pleocytosis, hypoglycorrhachia, abnormally elevated protein content, and organisms visualized on gram stain smear. In children with bacterial meningitis not receiving antibiotic therapy at the time of evaluation, CSF differential cell count with relative lymphocytosis is rare.     

Neonatal Gram negative meningitis: A 10-year review, with reference to outcome and relapse of infection

Twenty-four infants treated for neonatal Gram negative bacillary meningitis over a 10-year period were reviewed to determine the mortality and incidence of complications including relapse. Nine (37.5%) infants died; two survivors had major and 13 minimal or no handicap. Five (21%) infants had a relapse of meningitis after the initial course of treatment; two of these infants had been treated with cefotaxime. The outcome did not correlate with age, sex, gestation, cerebrospinal fluid (CSF) parameters or peripheral neutrophil counts. A poor outcome was associated with thrombocytopenia, persistence of viable organisms in the CSF for more than 24 h and with seizures, particularly in infants aged 7 days or less. There were no clinical or laboratory parameters predictive of subsequent relapse and there was no apparent relationship with choice or dose of antibiotic used or duration of treatment.     

Mycoplasma hominis. A cause of neonatal meningitis.

Two cases of Mycoplasma hominis meningitis in the newborn are described. These infants demonstrate the need to consider M. hominis as a cause of neonatal meningitis, especially if the Gram stain is negative, conventional cultures yield no growth, and there is a history of maternal infection. CSF cultures on appropriate medium can quickly confirm the diagnosis.