Epidemiology and diagnosis of viral and bacterial central nervous system infections in Sri Lanka: A Narrative review

Bacterial central nervous system (CNS) infections are life-threatening diseases with high mortality and long-term neurological sequels, while viral CNS infections are mild and self-limited. In Sri Lanka, 1000-1500 and 150-250 patients with meningitis and encephalitis respectively are reported annually to the Epidemiology Unit. Haemophilus influenzae, Group B Streptococcus, Streptococcus pneumoniae, Escherichia coli, Mycobacterium tuberculosis, Neisseria meningitidis, Group D Streptococcus, Leptospira borgpetersenii serovar Tarasssovi, Listeria monocytogenes, Streptococcus bovis biotype 2, enterovirus, Herpes Simplex Virus type 1 and type 2, Varicella zoster virus and cytomegalovirus have been reported up to 2022 in patients with meningitis while dengue virus, Japanese encephalitis virus, Varicella zoster virus, West Nile virus, Human Bocavirus Type 1, 2 and 3, human adenovirus type 41, Echovirus type 9 and 25, Herpes Simplex Virus type 1 and Mycoplasma pneumoniae have been reported in patients with encephalitis and meningoencephalitis. However less than 10% of cases have a definitive aetiological diagnosis with conventional bacterial culture methods routinely used to diagnose bacterial CNS infections, while molecular assays are used only for selected common viral pathogens in government hospitals in Sri Lanka. Use of antibiotics prior to cerebrospinal fluid collection, delay in sample collection, and low volume of samples have been identified as factors for low sensitivity of test results. Scientists, microbiologists and virologists are responsible for developing new test methods to identify current and previously unidentified causative microorganisms to extend the spectrum of neurotropic organisms in Sri Lanka to enhance the aetiological diagnosis.