What is the initial evaluation and management of multiple patients presenting simultaneously with nausea, vomiting, and headache, considering a possible shared exposure or infectious cause?

Multiple Patients with Nausea, Vomiting, and Headache: Mass Casualty Evaluation

When multiple patients present simultaneously with nausea, vomiting, and headache, immediately activate mass casualty protocols and consider shared environmental exposure (carbon monoxide, foodborne toxins, infectious outbreak) or bioterrorism as the primary differential until proven otherwise.

Immediate Triage and Scene Safety

Ensure scene safety first—do not enter the environment where patients became ill until hazardous materials teams clear the area. 1

• Establish a triage area outside the contaminated zone
• Implement standard, contact, and droplet precautions for all healthcare workers 1
• Separate patients by severity using ABCDE protocol: assess airway, breathing, circulation, disability (neurologic status), and exposure 2
• Document the temporal relationship of symptom onset across all patients 1

Critical Red Flag Assessment for Each Patient

The constellation of fever, altered mental status, headache, nausea, and vomiting mandates immediate consideration of CNS infection (meningitis/encephalitis) or intracranial hemorrhage. 1

Life-Threatening Presentations Requiring Immediate Intervention:

• Altered consciousness, seizures, or focal neurological deficits: Suggests encephalitis, meningitis, or intracranial hemorrhage requiring urgent non-contrast head CT 1, 3
• Fever >37.5°C with progressive neurological deterioration: 83% correlation with poor outcomes in intracerebral hemorrhage with ventricular extension 3
• Nuchal rigidity (neck stiffness) with headache: Cannot exclude meningitis even without fever—CSF analysis is the principal diagnostic contributor 2
• "Worst headache of life" or thunderclap onset: 80% of subarachnoid hemorrhage patients describe this; obtain immediate CT (98-100% sensitivity in first 12 hours) 2, 4
• Progressive symptoms over minutes to hours while active: Characteristic of intracerebral hemorrhage rather than ischemic stroke 3

Shared Exposure Investigation

Obtain detailed exposure history from all patients simultaneously to identify common sources. 1

Essential Historical Elements:

• Shared location/activity: Were all patients in the same building, event, or consumed the same food? 1
• Timing of symptom onset: Simultaneous onset suggests toxic exposure; staggered onset over days suggests infectious outbreak 1
• Travel history: Recent travel to areas with arboviral encephalitis, malaria, or other endemic infections 1
• Animal/vector exposure: Mosquito/tick bites (arboviruses, Lyme disease), bat exposure (rabies, Nipah virus), pig exposure (Nipah virus) 1
• Vaccination status: Unvaccinated individuals at risk for measles, mumps, enterovirus outbreaks 1
• Immunocompromise or HIV risk factors: Increases susceptibility to opportunistic CNS infections 1

Specific Infectious Outbreak Patterns:

• Enterovirus outbreaks: Peak in late summer/early fall; enterovirus 71 causes rhombencephalitis with myoclonus, tremors, ataxia 1
• Mumps: 50% have preceding parotitis; causes aseptic meningitis more commonly than encephalitis 1
• Foodborne illness: Nausea/vomiting/diarrhea without fever suggests toxin-mediated gastroenteritis 5, 6

Initial Diagnostic Workup for Each Patient

Prioritize investigations based on clinical presentation severity and suspected etiology. 1

Immediate Laboratory Testing:

• Complete blood count, comprehensive metabolic panel, liver function tests: Assess for metabolic abnormalities, dehydration, hepatic involvement 5, 7
• Urinalysis and urine pregnancy test (women of childbearing age): Exclude pregnancy and urinary tract infection 5, 7
• Blood cultures if febrile: Rule out systemic sepsis 1
• Serum glucose and electrolytes: Hypoglycemia and electrolyte disturbances cause altered mental status 1
• Arterial blood gas if altered consciousness: Assess for acidosis or metabolic derangement 1

Neuroimaging Indications:

• Non-contrast head CT immediately if any of the following: altered consciousness, focal neurological signs, seizures, severe headache, nuchal rigidity 1, 3, 2
• If CT negative but clinical suspicion for SAH or meningitis remains: Proceed to lumbar puncture for CSF analysis (cell count, protein, glucose, gram stain, culture, xanthochromia) 1, 2

CSF Analysis When Indicated:

• CSF PCR for HSV, enteroviruses, and other viral pathogens: More sensitive than culture for viral encephalitis 1
• CSF culture: Positive in 17-58% of mumps cases 1
• Serologic testing: For measles, mumps, arboviruses if epidemiologically relevant 1

Respiratory and Gastrointestinal Specimens:

• Nasopharyngeal swab for viral culture, antigen detection, PCR: If respiratory symptoms present (influenza, COVID-19) 1
• Stool culture and PCR: For enterovirus, norovirus if diarrhea present 1
• COVID-19 testing: GI symptoms (nausea, vomiting, abdominal pain, diarrhea) occur in 7.8-14.9% of COVID-19 patients and may precede respiratory symptoms 1

Empiric Treatment Pending Diagnosis

Do not delay empiric treatment while awaiting diagnostic results in patients with suspected CNS infection or severe metabolic derangement. 1

For Suspected Bacterial Meningitis/Encephalitis:

• Immediate empiric antibiotics: Ceftriaxone 2g IV plus vancomycin 15-20 mg/kg IV plus acyclovir 10 mg/kg IV every 8 hours 1
• Add ampicillin if age >50 years or immunocompromised (Listeria coverage) 1
• Dexamethasone 10 mg IV before or with first antibiotic dose if bacterial meningitis suspected 1

For Symptomatic Management:

• Antiemetics: Ondansetron 8 mg IV/oral every 4-6 hours, promethazine 12.5-25 mg IV/oral every 4-6 hours, or prochlorperazine 5-10 mg IV every 6-8 hours 4, 7
• Fluid resuscitation: Aggressive IV hydration for dehydration 5, 7
• Seizure management: Benzodiazepines for active seizures; consider prophylactic antiepileptics if encephalitis confirmed 1

Specific Antiviral Therapy:

• Acyclovir 10 mg/kg IV every 8 hours: For HSV encephalitis (strongly recommended even if PCR pending) 1
• Oseltamivir 75 mg oral twice daily: For influenza with neurological complications 1
• Ribavirin: Investigational for measles, Nipah virus, Hendra virus (contact CDC Special Pathogens Branch) 1

Public Health Notification

Immediately notify local public health authorities when multiple patients present with similar symptoms suggesting outbreak or bioterrorism. 1

• Report suspected arboviral encephalitis, measles, mumps, or other notifiable diseases 1
• Contact CDC Special Pathogens Branch for suspected Nipah, Hendra, or other emerging pathogens 1
• Implement infection control measures: isolation precautions, contact tracing, prophylaxis for exposed individuals 1

Common Pitfalls to Avoid

• Do not dismiss vomiting with headache as simple gastroenteritis when multiple patients are affected—this combination demands immediate investigation for shared toxic or infectious exposure 3, 5
• Do not assume absence of fever excludes meningitis—clinical characteristics have limited diagnostic accuracy, and CSF analysis remains essential 2
• Do not delay lumbar puncture if CT is negative but clinical suspicion for CNS infection remains high—up to 12% of SAH cases are initially misdiagnosed 2
• Do not overlook COVID-19 as a cause of GI symptoms—nausea, vomiting, and diarrhea may precede respiratory symptoms by several days 1
• Do not enter a potentially contaminated environment without proper hazmat clearance—carbon monoxide, chemical agents, and bioterrorism agents can incapacitate healthcare workers 1