6.3 Infectious Diseases
Key Takeaways
- Bacterial meningitis shows neutrophil-predominant CSF with markedly elevated protein and low glucose; viral meningitis shows lymphocyte predominance with normal glucose
- Septic arthritis presents as an acutely hot, red, monoarticular joint — arthrocentesis is mandatory before attributing symptoms to crystals or mechanical strain
- Osteomyelitis in children seeds the metaphysis of long bones; MRI is the most sensitive early imaging study because plain radiographs lag 10–14 days
- Infectious mononucleosis causes splenomegaly — contact sports must be avoided for about three to four weeks because of splenic rupture risk, and ampicillin produces a morbilliform rash
- qSOFA scores sepsis risk using respiratory rate greater than or equal to 22, altered mentation, and systolic blood pressure less than or equal to 100 mmHg — a febrile, tachycardic, confused patient needs emergency referral, not a walk-in adjustment
Why Infectious Disease Matters on Part II
Infectious disease questions on NBCE Part II test your ability to localize a pattern (bacterial versus viral), interpret a cerebrospinal fluid (CSF) profile, recognize musculoskeletal infections that change chiropractic management, and identify when a febrile patient is becoming septic and needs emergency referral. A chiropractor's office is not an emergency department, but Part II expects you to know which walk-in presentations are adjustment candidates and which are 911 or urgent-care cases.
As a general rule, bacterial infections produce high fever, neutrophilic leukocytosis with a left shift (bands), purulent secretions, and focal findings; viral infections produce lower-grade fever, lymphocytic predominance, and diffuse, self-limited illness. Atypical bacteria (Mycoplasma, Legionella) blur this. Use the pattern as a first sort, then confirm with the specific test.
Meningitis
Meningitis presents with fever, severe headache, nuchal rigidity (neck stiffness), and photophobia. Meningeal signs include:
- Kernig sign: with the hip flexed to 90 degrees, passive knee extension is painful or limited
- Brudzinski sign: passive neck flexion causes involuntary flexion of the hips and knees
CSF interpretation is a guaranteed exam topic:
| CSF Finding | Bacterial | Viral |
|---|---|---|
| Opening pressure | Elevated | Normal |
| WBC | Thousands, neutrophil-predominant | Less than 300, lymphocyte-predominant |
| Protein | Markedly elevated | Normal to mildly elevated |
| Glucose | Low (low CSF-to-serum ratio) | Normal |
| Gram stain | Often positive | Negative |
Common pathogens by age: neonates — group B Streptococcus, E. coli, Listeria; children and adults — Streptococcus pneumoniae and Neisseria meningitidis (the latter causing petechial or purpuric rash and meningococcemia with Waterhouse-Friderichsen adrenal hemorrhage). Suspected bacterial meningitis is an emergency — blood cultures and antibiotics immediately; do not delay treatment for imaging unless focal signs or papilledema suggest mass effect. A patient with fever, severe headache, and neck stiffness is not a cervical adjusting candidate.
Musculoskeletal Infections
- Osteomyelitis: in children, hematogenous seeding favors the metaphysis of long bones (rich, slow-flowing capillary loops); Staphylococcus aureus is the most common organism at all ages. Salmonella is classically associated with sickle cell disease; diabetic foot ulcers cause contiguous osteomyelitis (often polymicrobial). Plain radiographs lag 10–14 days behind infection (periosteal reaction, then lytic destruction); MRI is the most sensitive early imaging study. Elevated ESR and CRP support the diagnosis
- Septic arthritis: an acutely hot, red, exquisitely painful monoarticular joint with restricted range of motion. The rule: tap the joint — arthrocentesis with Gram stain, culture, and crystal analysis. Synovial WBC greater than 50,000 per mm³ (neutrophil-predominant) strongly suggests infection; S. aureus is most common overall, while Neisseria gonorrhoeae causes migratory arthritis and tenosynovitis in young, sexually active adults. Septic arthritis is a joint-destroying emergency requiring drainage and IV antibiotics — refer; do not adjust
Respiratory and Systemic Infections
- Pneumonia: typical (S. pneumoniae) — high fever, purulent sputum, lobar consolidation, neutrophilia; atypical (Mycoplasma, viral) — dry cough, diffuse or interstitial infiltrates worse than the physical exam (walking pneumonia)
- Tuberculosis: caused by Mycobacterium tuberculosis. Latent TB is asymptomatic, non-contagious, with positive PPD or IGRA and normal chest film. Active TB produces productive cough, hemoptysis, night sweats, weight loss, low-grade fever, and apical cavitary infiltrates on chest radiograph. The Ghon complex (peripheral lung focus plus hilar lymphadenopathy) marks primary infection
- Infectious mononucleosis: Epstein-Barr virus (EBV) — fatigue, exudative pharyngitis, posterior cervical lymphadenopathy, and splenomegaly. Labs show atypical lymphocytes and positive heterophile antibody (Monospot). Two board traps: giving ampicillin or amoxicillin produces a diffuse morbilliform rash, and splenomegaly mandates avoiding contact sports for about three to four weeks because of splenic rupture risk
- Influenza: abrupt fever, myalgias, headache, dry cough in winter. COVID-19 ranges from asymptomatic to severe viral pneumonia with ground-glass opacities; loss of taste or smell and multisystem inflammatory syndromes are recognized features
Childhood Exanthems, Zoster, and Fungal Infections
| Disease | Agent | Signature |
|---|---|---|
| Measles (rubeola) | Paramyxovirus | Koplik spots, the three Cs (cough, coryza, conjunctivitis), rash spreads head to toe |
| Rubella | Togavirus | Forchheimer spots, posterior auricular lymphadenopathy; teratogenic in pregnancy |
| Roseola | HHV-6 | High fever for three to five days, then rash as fever breaks |
| Varicella | VZV | Dew-drop-on-a-rose-petal vesicles in different stages simultaneously |
| Fifth disease | Parvovirus B19 | Slapped-cheek rash, then lacy reticular body rash |
Herpes zoster (shingles) is reactivation of varicella-zoster virus from dorsal root ganglia: painful grouped vesicles in a single dermatome that does not cross the midline. Hutchinson sign (vesicles on the tip or side of the nose) indicates nasociliary (V1) involvement and risk of herpes zoster ophthalmicus — refer urgently. Ramsay Hunt syndrome is zoster of the geniculate ganglion (facial palsy plus ear vesicles). Postherpetic neuralgia is the most common complication, especially in older adults — chiropractic supportive care may help after acute infection resolves, but acute zoster near the eye is a referral case.
Candida causes oral thrush and esophagitis in the immunocompromised. Tinea (dermatophytes) produces annular ringworm with central clearing; diagnosis by KOH preparation showing hyphae.
Sepsis and Chiropractic Red Flags
Sepsis is life-threatening organ dysfunction from a dysregulated response to infection. The quick bedside screen is qSOFA (one point each):
- Respiratory rate greater than or equal to 22 per minute
- Altered mentation (Glasgow Coma Scale less than 15)
- Systolic blood pressure less than or equal to 100 mmHg
A qSOFA score of 2 or more signals high risk of death or prolonged ICU stay. The older SIRS criteria (temperature above 38 °C or below 36 °C, heart rate above 90, respiratory rate above 20, WBC above 12,000 or below 4,000) plus a suspected source define systemic inflammatory response; elevated lactate (greater than 2 mmol/L) refines severity.
For the practicing chiropractor: a patient with fever, tachycardia, tachypnea, and confusion is not a walk-in adjustment — they need emergency evaluation. Likewise, hot monoarticular joints, meningeal signs, and acute zoster with Hutchinson sign all mandate referral.
Takeaways: low CSF glucose equals bacterial (or fungal or TB); normal glucose equals viral; MRI, not plain film, detects early osteomyelitis; monoarticular hot joint equals tap it before blaming crystals; Koplik spots precede the measles rash; roseola rash follows the fever; and qSOFA uses respiratory rate, mentation, and systolic pressure — not temperature or heart rate alone.
A 19-year-old college student has fever, severe headache, neck stiffness, and photophobia. CSF shows 2,800 WBC per mm³ with 88% neutrophils, protein of 220 mg/dL, and glucose of 28 mg/dL (serum glucose 95 mg/dL). Which management principle applies?
A 6-year-old boy has fever and refusal to bear weight on his right leg for five days. Plain radiograph of the tibia is normal, but he has elevated ESR and focal tenderness over the proximal tibia metaphysis. Which study is most appropriate to detect early osteomyelitis?
A 17-year-old with confirmed infectious mononucleosis wants to return to varsity football two weeks after symptom onset. Examination shows a palpable spleen tip 2 cm below the costal margin. What is the appropriate advice?
A 58-year-old woman with a urinary tract infection now has fever of 39.4 °C, respiratory rate of 26 per minute, systolic blood pressure of 88 mmHg, and confusion. Her qSOFA score is 3. What is the most appropriate action in a chiropractic office setting?