# Acute Bacterial Meningitis > Acute bacterial meningitis for NEET-PG Medicine: CSF patterns, empirical antibiotics by age, dexamethasone timing, LP criteria and contact prophylaxis. - Canonical URL: https://prepelephant.com/topics/neet-pg/medicine/acute-bacterial-meningitis - Exam / course: NEET-PG · Subject: Medicine - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-08 - Last updated: 2026-10-08 - Reference basis: Harrison's Principles of Internal Medicine; Davidson's Principles and Practice of Medicine; Ghai Essential Pediatrics - How to cite: "Acute Bacterial Meningitis", PrepElephant, https://prepelephant.com/topics/neet-pg/medicine/acute-bacterial-meningitis ## Direct answer Acute bacterial meningitis is bacterial infection of the leptomeninges, usually Streptococcus pneumoniae or Neisseria meningitidis in adults, producing a neutrophil-rich CSF with low glucose and high protein. Empirical antibiotics must not wait for lumbar puncture, dexamethasone is given before or with the first antibiotic dose, and close contacts of meningococcal cases need chemoprophylaxis. ## What you must remember - **Bacterial CSF pattern:** turbid fluid, neutrophil-predominant pleocytosis often above 1000 cells per microlitre, a CSF to blood glucose ratio below about 0.4, and raised protein. - **Viral and TB patterns:** viral meningitis shows lymphocytosis with normal glucose; tuberculous meningitis shows lymphocytosis, low glucose, high protein and a fibrin web. - **Organisms by age:** Streptococcus pneumoniae and Neisseria meningitidis in adults, Group B streptococcus, Escherichia coli and Listeria in neonates, and Listeria added for age 50 and over. - **Empirical antibiotics:** a third-generation cephalosporin such as ceftriaxone, with vancomycin where ceftriaxone-resistant pneumococcus is a realistic concern, and ampicillin added where Listeria is possible. - **Dexamethasone:** 0.15 mg/kg every six hours for two to four days, given before or with the first antibiotic dose; benefit is best established in pneumococcal disease. - **Lumbar puncture criteria:** CT before LP if focal deficit, papilloedema, seizure, reduced consciousness or immunosuppression; blood cultures and antibiotics come first if LP is delayed. - **Contacts:** rifampicin 600 mg twice daily for two days for adult contacts of meningococcal disease, or single-dose ciprofloxacin or ceftriaxone when rifampicin is unsuitable; Haemophilus influenzae type b contacts also qualify. - **Vaccination:** Hib and pneumococcal conjugate vaccines are part of the Indian schedule, and meningococcal vaccines are used for at-risk groups and travellers. ## Worked example: fever, neck stiffness and a non-blanching rash A 23-year-old student arrives with fever, neck stiffness and a rash that does not fade under a glass. He is haemodynamically unstable, so meningococcal sepsis is the working diagnosis until proved otherwise. 1. **Give antibiotics first:** Blood cultures are drawn, and high-dose ceftriaxone is given without waiting for imaging or lumbar puncture, since delay costs lives. 2. **Give dexamethasone:** Dexamethasone is given with or just before that first dose. 3. **Decide on lumbar puncture:** He is alert but unwell, with no focal deficit, papilloedema or seizure, so CT is not required before lumbar puncture. The procedure is done once he is stable and clotting status is checked. 4. **Read the CSF:** The CSF shows neutrophil-predominant pleocytosis with low glucose and high protein, and Gram stain and PCR add diagnostic yield. 5. **Manage contacts:** Because he lives in a hostel, close contacts are identified and given rifampicin, since the disease spreads in closed communities, and the public health authority is notified. 6. **Review the treatment:** Antibiotic choice is reviewed once culture and sensitivities return, and the total course depends on the organism. If he deteriorates, the team reconsiders the diagnosis, looks for complications such as hydrocephalus or raised pressure, and repeats CSF studies where needed. ## Where the examiner tests the timing Meningitis questions are mostly about sequence and timing. - **Trap:** Ordering CT and lumbar puncture before antibiotics. — **Correct:** Antibiotics are given first in every suspected case, with cultures drawn if that does not delay treatment. - **Trap:** Skipping the CT check before lumbar puncture. — **Correct:** CT comes first with a focal deficit, papilloedema, seizure, reduced consciousness or immunosuppression. - **Trap:** Relying on Kernig and Brudzinski signs. — **Correct:** Both signs are insensitive, particularly in infants and the elderly, so their absence does not exclude meningitis. - **Trap:** Applying dexamethasone evidence to every cause. — **Correct:** Its benefit is firmest in pneumococcal disease, so the indication should be checked rather than assumed. ## Frequently asked questions ### What CSF findings suggest bacterial meningitis? Bacterial meningitis gives turbid CSF with neutrophil-predominant pleocytosis, a CSF to blood glucose ratio below about 0.4 and raised protein. Gram stain and culture then identify the organism, whereas viral meningitis typically shows lymphocytes with normal glucose. ### Why must antibiotics not wait for lumbar puncture in suspected meningitis? Antibiotics must not wait for lumbar puncture in suspected bacterial meningitis because the delay increases mortality and neurological damage. Blood cultures are taken first if they do not delay treatment, and lumbar puncture follows once the patient is stable and CT criteria are met. ### When is dexamethasone given in bacterial meningitis? Dexamethasone is given in bacterial meningitis before or with the first antibiotic dose, at 0.15 mg/kg every six hours for two to four days. Its benefit in reducing neurological sequelae is best established in pneumococcal meningitis. ### Who needs rifampicin prophylaxis after meningococcal disease? Close contacts of a meningococcal case, such as household members and hostel mates, need rifampicin prophylaxis at 600 mg twice daily for two days for adults. Single-dose ciprofloxacin or ceftriaxone is an alternative where rifampicin is unsuitable. ### When is vancomycin added to empirical meningitis treatment? Vancomycin is added to empirical therapy where ceftriaxone-resistant pneumococci are a realistic concern, guided by local resistance patterns and the patient's risk. Ceftriaxone remains the backbone of treatment, and the addition is a deliberate choice rather than routine.