Value of antigen quantitation in Haemophilus influenzae type b meningitis

Detection of antigenuria for diagnosis of invasive Haemophilus influenzae type b disease

BACKGROUND

Haemophilus influenzae type b (Hib) diseases are responsible for an estimated 400,000 childhood deaths, mostly in developing countries.

OBJECTIVES

To determine the value of the Wellcogen quantitative latex agglutination test (LA) in urine for the diagnosis of Hib pneumonia and meningitis.

METHODS

Healthy and sick children aged <5 y were enrolled in Dhaka Shishu (Children's) Hospital. Boiled and non-concentrated urine specimens underwent LA testing. In vaccinated subjects, urine was tested by LA at 24 h, 4-6 and 7-10 d after vaccination.

RESULTS

Of 1302 enrolled cases, 201 were healthy (90 Hib vaccine recipients and 111 provided NP) and 1101 were sick with either pneumonia (n=974) or meningitis (n=127). Among the healthy children enrolled, 41 (41/111, 37%) were colonised with Hib and two (2/41, 5%) were positive by LA test. Hib antigenuria among the children who had received Hib vaccination was mainly detected only on day 1 (7/90, 8%) of vaccination. Among the sick children, LA test for Hib antigen was positive for all confirmed cases of Hib pneumonia (10) and meningitis (35). In contrast, none of the urine specimens from the cases with a known aetiology other than Hib (n=104) was positive. Quantitative analysis of antigenuria of sick children showed that it is positive at least up to 1:8 and 1:16 dilutions for pneumonia and meningitis, respectively, in contrast with <or=1:4 for healthy children. In addition to the ten cases of culture-proven Hib, the test detected an additional 16 Hib pneumonia cases among children diagnosed as pneumonia, based on the presence of antigenuria >or=1:8 dilutions.

CONCLUSIONS

The Wellcogen LA test for Hib using boiled and non-concentrated urine is more sensitive than blood culture alone and is highly specific.

Haemophilus influenzae meningitis with prolonged hospital course

A retrospective evaluation of Haemophilus influenzae type b meningitis observed over a 2-year period documented 86 cases. Eight of these patients demonstrated an unusual clinical course characterized by persistent fever (duration: greater than 10 days), cerebrospinal fluid pleocytosis, profound meningeal enhancement on computed tomography, significant morbidity, and a prolonged hospital course. The mean age of these 8 patients was 6 months, in contrast to a mean age of 14 months for the entire group. Two patients had clinical evidence of relapse. Four of the 8 patients tested for latex particle agglutination in the cerebrospinal fluid remained positive after 10 days. All patients received antimicrobial therapy until they were afebrile for a minimum of 5 days. Subsequent neurologic examination revealed a persistent seizure disorder in 5 patients (62.5%), moderate-to-profound hearing loss in 2 (25%), mild ataxia in 1 (12.5%), and developmental delay with hydrocephalus which required shunting in 1 (12.5%). One patient had no sequelae.

Serious bacterial infections. C-reactive protein as a serial index of severity

The clinical course of 72 septicemic episodes or focal severe bacterial infections was monitored by daily measurements of serum C-reactive protein (CRP) in 59 children beyond the neonatal period, 19 of whom were immunocompromised. CRP was determined quantitatively by an immunoturbidimetric method from a finger prick sample until either clinical recovery occurred and antimicrobial therapy was discontinued or until the death of the patient. The primarily elevated CRP levels (greater than or equal to 20 mg/l) usually increased about for a day but then decreased rapidly, provided the patient recovered uneventfully. If not, CRP remained at a high level or reincreased after transient decrease. Behaviour of CRP was not affected by the immunologic status of the patient. This property makes CRP especially useful in immunocompromised patients in whom other commonly used laboratory parameters may fail.

Prospective evaluation of bacterial antigen detection in cerebral spinal fluid in the diagnosis of bacterial meningitis in a predominantly adult hospital

The results of all CSF latex agglutination (LA) tests performed in a large predominantly adult hospital over 1 yr are reviewed. Eight cases of bacterial meningitis were recognized during this time, and of these only three were due to organisms detectable by commercially available LA kits. In one case, the LA was uninterpretable, and in the second the LA was not performed because less than 5 x 10(6) WBC/L were seen in the CSF. In the third case the Gram stain was positive. No cases of partially treated meningitis were diagnosed. In this setting, the LA test did not contribute significantly to patient management.

Early synergistic killing activity at concentrations attainable in CSF of amoxicillin or cefotaxime and aminoglycosides against Haemophilus influenzae

Rapid eradication of bacteria from the CSF is critical for the outcome of Haemophilus influenzae meningitis in children. In 15 patients studied, the mean H. influenzae colony counts in CSF were 10(5) CFU/ml (range: 10(2) to 10(9) CFU/ml). Time-kill curves were determined for amoxicillin and cefotaxime alone and in combination with gentamicin or amikacin, against 60 clinical isolates of H. influenzae at concentrations equivalent to those found in CSF following systemic administration. Against beta-lactamase-negative strains (n = 44) a bactericidal effect was observed at 18 h for amoxicillin alone, at 5 h for amoxicillin plus aminoglycosides and at 2.5 h for cefotaxime with or without aminoglycosides. Against beta-lactamase-positive strains a bactericidal effect was observed at 18 h for cefotaxime, at 5 h for amoxicillin plus aminoglycosides and at 2.5 h for cefotaxime plus aminoglycosides. It appears that despite low concentrations of gentamicin or amikacin in the CSF, the accelerated killing of H. influenzae provides a rationale for the initial use of the combination of cefotaxime and aminoglycosides in the initial treatment of H. influenzae meningitis.

Use of rapidly generated results in patient management

The usefulness of a rapid diagnostic test in patient management depends on the sensitivity of the test, the clinical consequences of false-negative or false-positive results, the ease and cost of performance, and the timely availability of results. A test that is sensitive, specific, inexpensive, and rapid is presumed to be useful clinically. However, there has been surprisingly little effort to measure the actual impact of the results on patient care. Since antigen detection for Haemophilus influenzae type b disease has been available for more than a decade, it will be used as a model to illustrate several factors that help determine the benefits, limitations, and pitfalls of antigen detection in the management of patients with serious bacterial infections. Herein we will compare the use of antigen detection in meningitis with that in other Haemophilus influenzae type b diseases. We also will review our experience with the impact of rapid diagnosis on the treatment of bacterial meningitis. Finally, other factors that influence the usefulness of antigen detection on patient care will be explored by comparing the potential consequences of laboratory error on the management of patients with Haemophilus influenzae type b infections with that of management of other kinds of infections, such as streptococcal pharyngitis, sexually transmitted diseases, and viral respiratory infections.

Cerebrospinal fluid cultures and analysis

Prompt and accurate diagnosis of acute central nervous system infections is of vital importance to the emergency physician. With the advent of modern antimicrobial therapy, the nearly uniformly fatal outcome of untreated bacterial meningitis can be reduced substantially. Proper test selection is crucial in arriving at a correct and timely diagnosis. A variety of tests are currently available for evaluation of the patient with an acute central nervous system infection. We review the current state of the art in central nervous system testing. Cost considerations and an algorithm for efficient selection of appropriate tests are presented.

Cerebrospinal fluid white cell, glucose and protein changes during the treatment of Haemophilus influenzae meningitis

298 cerebrospinal fluid (CSF) samples obtained from 116 children with ongoing Haemophilus influenzae meningitis were analyzed in order to determine the kinetics of the white blood cell (WBC) count and the glucose and protein concentrations--parameters for which there are no "reference values" available for the convalescence period of meningitis. The values determined during the first 10 days of treatment are presented as percentile distribution graphs. CSF WBC counts increased slightly for the first 24 h but declined thereafter without reaching, however, the normal value (less than or equal to 5/microliter) within 10 days in the majority of cases. Low CSF glucose concentrations usually increased to a normal or almost normal level within 48 h. CSF protein concentrations declined steadily throughout the treatment. Extremely high CSF WBC or low CSF glucose concentrations suggested neurological complications or treatment failure. The value of sequentially determined CSF WBC, glucose and protein in monitoring recovery from H. influenzae meningitis is, however, so vague that routine spinal taps do not seem indicated after CSF has become sterilized.