CNS & Travel/Emerging Infections
CSF that names the bug, and the returning-traveler fever workup
Meningitis: recognition and the first hour
Presentation. Bacterial meningitis causes fever, headache, nuchal rigidity, photophobia and altered mental status; Kernig and Brudzinski signs support the diagnosis. The classic triad of fever, neck stiffness and altered mentation is only modestly sensitive, so treat on suspicion. A petechial or purpuric rash suggests Neisseria meningitidis.
CT before LP? Obtain head CT first only if the patient is immunocompromised or has a focal neurologic deficit, new seizure, papilledema or markedly depressed consciousness. Otherwise do the lumbar puncture first. Either way, never delay antibiotics or dexamethasone for imaging; pretreatment lowers culture yield but leaves the cell count and chemistry interpretable.
- Blood culturesdraw immediately
- Dexamethasone + empiric antibioticsdo not delay for CT; no steroid in neonates or shunt or post-neurosurgical cases
- CT if indicated, then LPfocal deficit, immunocompromise, seizure, papilledema, coma
- Tailor to CSF and culturenarrow therapy; continue the steroid only for pneumococcus
CSF interpretation and empiric therapy
| Feature | Bacterial | Viral | Fungal or TB |
|---|---|---|---|
| Cells | Neutrophils, often thousands | Lymphocytes | Lymphocytes |
| Glucose | Low: under 40 mg/dL, CSF:serum under 0.4 | Normal | Low |
| Protein | High, often over 200 mg/dL | Mildly high | High |
| Opening pressure | High | Normal or mildly high | High, especially cryptococcal |
| Confirming tests | Gram stain, culture | Enterovirus or HSV PCR | Cryptococcal antigen; AFB smear, culture, PCR |
- Neonates: group B strep, E. coli and Listeria; ampicillin plus cefepime or ceftazidime (or gentamicin), since cefotaxime is no longer available in the US, avoiding ceftriaxone, which displaces bilirubin.
- Children and adults: S. pneumoniae and N. meningitidis; vancomycin plus ceftriaxone, with vancomycin covering resistant pneumococcus.
- Age over 50, immunocompromise, alcoholism or pregnancy: add ampicillin for Listeria monocytogenes.
- Neurosurgery or shunt: staphylococci and gram-negative rods; vancomycin plus cefepime or meropenem.
Dexamethasone. Give it just before or with the first antibiotic dose. By blunting the inflammatory surge from bacterial lysis, it lowers mortality and hearing loss, especially with S. pneumoniae (and H. influenzae in children). Continue it only if pneumococcus is confirmed. Do not give it to neonates or for meningitis after neurosurgery or with a shunt.
Other forms. Close contacts of meningococcal disease receive rifampin, ciprofloxacin or ceftriaxone prophylaxis (avoid ciprofloxacin where resistant strains have been reported; prior vaccination does not remove the need), and the patient stays on droplet precautions for the first 24 hours of therapy. Viral meningitis, most often enteroviral in summer and fall, is managed supportively. Cryptococcal meningitis in advanced HIV is treated with amphotericin B plus flucytosine, with serial LPs for high opening pressure.
Encephalitis and brain abscess
HSV encephalitis. HSV-1 causes fever with altered behavior, aphasia or seizures from hemorrhagic necrosis of the temporal lobe. MRI shows temporal-lobe changes, and CSF shows lymphocytes with red cells; CSF HSV PCR confirms. Start IV acyclovir empirically without waiting for the PCR, because delay costs lives, and hydrate to prevent acyclovir crystal nephropathy.
Temporal-lobe hemorrhagic necrosis plus RBCs in the CSF is HSV until proven otherwise.
Brain abscess. A ring-enhancing lesion with surrounding edema, usually from contiguous spread (otitis, sinusitis, dental infection) or hematogenous seeding (endocarditis, right-to-left shunts). It is often polymicrobial, with viridans streptococci and anaerobes. Headache dominates and fever is often absent. Treat with aspiration or drainage plus antibiotics (typically ceftriaxone plus metronidazole), and avoid LP because of herniation risk.
Ring lesions in HIV. With CD4 below 100, multiple ring-enhancing lesions point to Toxoplasma gondii (pyrimethamine, sulfadiazine and leucovorin); a lesion that fails to shrink after 2 weeks of treatment suggests primary CNS lymphoma.
The febrile returning traveler
Approach. Fever after tropical travel is malaria until proven otherwise; send thick and thin smears at once and repeat them if negative. Typhoid and dengue complete the core differential.
| Feature | Malaria | Typhoid fever | Dengue |
|---|---|---|---|
| Agent | Plasmodium, via Anopheles mosquitoes | Salmonella Typhi, fecal-oral | Flavivirus, via Aedes aegypti |
| Clues | Cyclic fevers; P. falciparum causes high parasitemia and cerebral malaria | Stepwise rising fever, relative bradycardia (Faget sign), truncal rose spots, abdominal pain, constipation before diarrhea | High fever, severe retro-orbital and bone ("breakbone") pain, rash, leukopenia, thrombocytopenia |
| Diagnosis | Giemsa thick and thin smears | Blood cultures | NS1 antigen or PCR early, IgM later |
| Treatment | Species-directed; primaquine or single-dose tafenoquine (G6PD activity at least 70%) for P. vivax and P. ovale | Ceftriaxone or a fluoroquinolone | Supportive; avoid NSAIDs and aspirin |
| Danger | Cerebral malaria, organ failure | Intestinal perforation; chronic gallbladder carriage | Hemorrhagic fever and shock on a second heterotypic infection |
Malaria. The thick smear detects parasites and the thin smear identifies species and parasitemia; ring forms at high parasitemia with banana-shaped gametocytes mean P. falciparum. Severe falciparum malaria needs IV artesunate. P. vivax and P. ovale form dormant liver hypnozoites that cause relapse; primaquine eradicates them but can trigger hemolysis, so screen for G6PD deficiency first.
Typhoid and dengue. Fluoroquinolone resistance in Salmonella Typhi is now common in South Asia, and gallbladder carriage causes chronic shedding. Severe dengue after a second infection with a different serotype reflects antibody-dependent enhancement: non-neutralizing antibodies from the first infection increase viral uptake. Chikungunya (severe polyarthralgia) and Zika (rash, conjunctivitis, congenital microcephaly) share the Aedes vector and overlap with dengue.
Tick-borne infections
| Disease | Organism, tick | Key findings | Treatment |
|---|---|---|---|
| Lyme disease | Borrelia burgdorferi, Ixodes | Erythema migrans target rash, then AV block, facial (Bell) palsy, migratory arthritis | Doxycycline (early disease, facial palsy, meningitis); IV ceftriaxone for hospitalized carditis with high-grade AV block |
| Rocky Mountain spotted fever | Rickettsia rickettsii, Dermacentor | Fever, headache, myalgia, then rash from wrists and ankles spreading centrally, including palms and soles | Doxycycline at any age, empirically |
| Ehrlichiosis | Ehrlichia chaffeensis, Lone Star tick | Fever, leukopenia, thrombocytopenia, high transaminases, usually no rash; morulae in monocytes | Doxycycline |
| Anaplasmosis | Anaplasma phagocytophilum, Ixodes | Same picture; morulae in granulocytes | Doxycycline |
| Babesiosis | Babesia microti, Ixodes | Hemolytic anemia with intraerythrocytic ring forms; severe after splenectomy | Atovaquone plus azithromycin |
Lyme disease. Erythema migrans is a clinical diagnosis, treated without serology, which is often negative early. Later manifestations are confirmed with ELISA followed by Western blot. Isolated facial palsy can be treated with oral doxycycline; IV ceftriaxone is used for hospitalized patients with high-grade AV block and is an option for Lyme meningitis.
RMSF. Despite its name, most cases occur in the southeastern and south-central United States, such as North Carolina. Doxycycline is started on suspicion, without waiting for serology, even in young children: the risk of untreated RMSF far outweighs dental staining from a short course.