Abstract:
The study focused on the sensitivity and specificity of cerebrospinal fluid
appearance and white blood cell (WBC) count as potential laboratory screening
indicators compared to culture method. This is because Cerebrospinal fluid (CSF)
culture facilities are expensive and difficult to maintain in resource poor laboratory
settings yet this is the gold standard for diagnosis. Early signs of meningitis are
often subtle and nonspecific resulting in unacceptably high mortality and morbidity
rates in children, especially those from developing countries where rapid access to
medical attention and resources is unavailable. Diagnosing acute bacterial
meningitis in children is likely to be missed in a third of cases at district hospitals
in sub-Saharan Africa where adequate and reliable laboratory resources are lacking.
Most affected patients now survive due to antibiotic use, though many children still
die or suffer permanent neurologic sequelae as a result of bacterial meningitis. Data
was gathered from samples collected from children aged below five years admitted
at the participating hospitals between the time periods 2001 to 2008. This was
carried out retrospectively from the period 2001 to 2005 and prospectively from
2006 to 2008. A total of 32,152 samples were collected for the entire period. Of the
29,153 samples collected with reported appearance, 4.49% of them were positive
for pathogenic organisms out of which three micro-organisms were of most interest
to the surveillance; Streptococcus pneumoniae, Haemophilus influenzae and
Neisseria meningitidis that accounted for 50.7% of the positive isolates. Turbid
appearance had a sensitivity of 72% (95% CI 69 – 74) and specificity of 96%.
Clear appearance had a sensitivity of 18% (95% CI 16.1 – 20.3) and a specificity of
xv
17%. White blood cell count greater than 5 (WBC>5) per microlitre had a
sensitivity of 81.5% (95% CI 77.2 - 85.3) and a specificity of 78.7%. White blood
cell count greater than 10 (WBC>10) per microlitre had sensitivity of 80.1% (95%
CI 75.7 – 84) and specificity of 91.3%. The 32,152 samples were also divided into
Pre- and Post- Hib eras to account for the introduction of the Haemophilus
influenzae type b vaccine that was introduced in the region. The pre-Hib, vaccine
era accounted for 26.8% of the samples of which 5.0% were culture positive. The
post-Hib data accounted for 73.2% of the total samples of which, 11.8% were
culture positive. Although the number of positive isolates in the pre and post Hib
eras varied significantly, there were insignificant differences in the sensitivities and
specificities of turbidity and white cell counts. The recommendation is that,
presence of a turbid sample is a good indicator of presence of an etiological agent.
However, using (one evaluation method) appearance alone is not adequate.
Additional use of white blood cell counts, as a screening criterion should be
included to increase the test sensitivity to a point where it is useful for surveillance.
The benefit of this study results is that this information can be used to advise
laboratory personnel on what minimum criteria can be used to analyze CSF
samples to reduce on missed cases and also maximize on the limited laboratory
resources.