A 35-year-old woman from San Francisco has been refusing to vaccinate her children due to the claims that vaccinations may cause autism in children. Her 10-year-old male child began developing a low-grade fever with a rash that started on his face; as the rash began to spread to his limbs, it slowly disappeared from his face. When the child was taken to a clinic, the physician noticed swollen lymph nodes behind the ears of the child. Which of the following are characteristics of the virus causing these symptoms?

Enveloped, SS + nonsegmented RNA

Enveloped, SS - nonsegmented RNA

A 4-month-old boy is brought to the physician by his parents for a well-child examination. He has cystic fibrosis diagnosed by newborn screening. His parents report frequent feedings and large-volume and greasy stools. His 4-year-old brother has autism. Current medications include bronchodilators, pancreatic enzyme supplements, and fat-soluble vitamins. He is at the 18th percentile for height and 15th percentile for weight. Scattered wheezes are heard throughout both lung fields. Examination shows a distended and tympanic abdomen with no tenderness or guarding. Which of the following is a contraindication for administering one or more routine vaccinations?

Fever of 38.2°C (100.7°F) following previous vaccinations

A 3000-g (6.6-lb) female newborn is delivered at term to a 23-year-old primigravid woman. The mother has had no prenatal care. Immunization records are not available. Cardiac examination shows a continuous heart murmur. There are several bluish macules on the skin that do not blanch with pressure. Slit lamp examination shows cloudy lenses in both eyes. The newborn does not pass his auditory screening tests. Which of the following is the most likely diagnosis?

Congenital parvovirus infection

Congenital cytomegalovirus infection

A 32-year-old pregnant woman at 32 weeks gestation presents with a 2-day history of low-grade fever, headache, and myalgias. She works at a daycare where several children recently had 'slapped cheek' rash. Laboratory studies show hemoglobin 8.5 g/dL (baseline 12 g/dL), reticulocyte count 0.1%, and positive parvovirus B19 IgM. Fetal ultrasound shows hydrops fetalis with ascites, pleural effusions, and severe anemia on cordocentesis. Evaluate the pathophysiologic mechanism and management approach that best addresses both maternal and fetal complications.

Vertical transmission causing fetal aplastic crisis; intrauterine transfusion with close monitoring

Fetal cardiac failure from myocarditis; deliver immediately for neonatal intensive care

Placental insufficiency from maternal viremia; administer antivirals and corticosteroids

Maternal immune thrombocytopenia causing fetal bleeding; administer IVIG to mother

Maternal-fetal ABO incompatibility exacerbated by viral infection; plasmapheresis

A public health official must design a vaccination strategy for a refugee camp with 10,000 children under 5 years old. Resources allow for only one vaccine initially. Current diseases in the camp include measles (15 cases/week), diphtheria (5 cases/week), pertussis (20 cases/week), and rotavirus diarrhea (100 cases/week). Three children have died from measles, two from pertussis, and ten from dehydration due to diarrhea. Evaluate which vaccine should be prioritized and justify the decision.

MMR vaccine because measles has the highest case fatality rate and transmission potential

DTaP vaccine because pertussis has the highest incidence

Oral rehydration therapy instead of vaccination to address immediate mortality

Rotavirus vaccine because diarrhea has caused the most deaths

Pneumococcal vaccine because it prevents the leading cause of childhood mortality globally

A hospital infection control committee reviews a cluster of 5 cases of invasive pneumococcal disease over 6 months, all caused by serotype 19A, in vaccinated children aged 3-5 years who received all recommended doses of PCV13. All isolates show resistance to penicillin and macrolides. The committee must evaluate the outbreak and recommend interventions. Which factor most likely explains this outbreak despite appropriate vaccination?

Serotype 19A strain with capsular switching evading vaccine-induced immunity

Serotype replacement with non-vaccine serotypes after PCV7 was replaced by PCV13

Evolution of antibiotic resistance in serotype 19A reducing vaccine effectiveness

Inadequate immune response in children with undiagnosed primary immunodeficiency

Vaccine storage failure leading to loss of immunogenicity

A 65-year-old man with diabetes mellitus and chronic kidney disease presents with sudden onset right-sided facial weakness, inability to close his right eye, and loss of taste on the anterior two-thirds of his tongue. He has vesicular lesions in his right external auditory canal. He received varicella vaccine 20 years ago and had shingles on his trunk 5 years ago. Analyze the relationship between his current presentation and his varicella vaccination history.

His previous shingles and current presentation both resulted from reactivation of wild-type VZV acquired before vaccination

The varicella vaccine virus has reactivated to cause this condition

This is a bacterial infection unrelated to varicella-zoster virus

The current infection represents primary varicella despite previous vaccination

Simultaneous reactivation of vaccine and wild-type VZV strains

Measles, mumps, rubella for USMLE Step 1: High-Yield Microbiology Lessons

Measles (Rubeola) - The 4 C's & 1 P

Virus: Paramyxovirus family; enveloped, single-stranded RNA virus.
Transmission: Respiratory droplets; highly contagious.
Prodrome: 📌 4 C's & 1 P
- Cough
- Coryza (rhinorrhea)
- Conjunctivitis
- Coplik (Koplik) spots: Pathognomonic blue-white spots on buccal mucosa.
- Photophobia

Koplik spots on buccal mucosa

⭐ Subacute sclerosing panencephalitis (SSPE) is a rare, fatal, progressive neurological disorder that can manifest 7-10 years after the initial measles infection.

Complications: Pneumonia (most common cause of death), otitis media, encephalitis.

Mumps - Puffy Face Problems

Cause: Mumps virus, an RNA paramyxovirus.
Transmission: Respiratory droplets; incubation period of 12-25 days.
Presentation: Prodrome of fever and malaise, followed by tender, bilateral (or unilateral) parotitis, causing the classic “puffy face.”
Complications:
- Orchitis: Inflammation of testes, common in post-pubertal males; may lead to impaired fertility.
- Pancreatitis: Can cause epigastric pain; check serum amylase.
- Deafness: Sensorineural, usually transient.

⭐ Aseptic meningitis is the most common extrasalivary gland complication.

Prevention: Live-attenuated MMR vaccine.

Rubella - Teratogen Terror

A Togavirus, transmitted via respiratory droplets. Maternal infection poses a significant risk to the fetus, especially during the first trimester.

Blueberry muffin rash on different skin tones

Clinical Features of CRS:

Sensorineural deafness (most common)
Ocular: Cataracts, retinopathy
Cardiac: Patent ductus arteriosus (PDA), pulmonary artery stenosis
CNS: Microcephaly, intellectual disability
Dermal: "Blueberry muffin" rash (dermal erythropoiesis)

⭐ Classic Triad of CRS:

Cataracts (or other eye defects)

Sensorineural Deafness

Congenital Heart Disease (esp. PDA)

Prevention: Live-attenuated MMR vaccine is key. Contraindicated in pregnancy.

MMR Vaccine - The Triple Shield

Type: Live attenuated vaccine containing measles, mumps, and rubella viruses.
Administration: Subcutaneous injection.
Schedule: Standard 2-dose series given at 12-15 months and 4-6 years. A catch-up dose can be given to unprotected adults.
Contraindications:
- Severe immunodeficiency (e.g., SCID, chemotherapy, CD4 count <200).
- Pregnancy (advise waiting 4 weeks to conceive post-vaccination).
- History of anaphylaxis to neomycin or gelatin.

⭐ MMR is NOT contraindicated in patients with egg allergy. The vaccine is grown in chick embryo fibroblasts, not whole eggs, and is considered safe.

High‑Yield Points - ⚡ Biggest Takeaways

Measles (Rubeola) presents with Cough, Coryza, Conjunctivitis (3 C's) and pathognomonic Koplik spots, followed by a descending maculopapular rash. A severe delayed complication is Subacute Sclerosing Panencephalitis (SSPE).

Mumps is characterized by parotitis, with potential complications of orchitis (leading to sterility), pancreatitis, and aseptic meningitis.

Rubella (German Measles) is typically mild but causes devastating Congenital Rubella Syndrome in fetuses, classically presenting with a triad of cataracts, deafness, and patent ductus arteriosus (PDA).

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