Microbiology integration paediatrics quiz questions

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Here is a comprehensive Microbiology-Integrated Paediatrics Quiz with 20 questions covering common examinable topics across infections, organisms, vaccines, and clinical management.

🧫 Microbiology Integration - Paediatrics Quiz

Section A: Single Best Answer (SBA)

Q1. A 3-day-old neonate presents with fever, poor feeding, bulging fontanelle and seizures. CSF shows low glucose, raised protein, and gram-positive diplococci. What is the MOST likely causative organism?

A) Listeria monocytogenes
B) Neisseria meningitidis
C) Streptococcus agalactiae (Group B Streptococcus)
D) Escherichia coli

Answer: C Explanation: Group B Streptococcus (GBS) is the leading cause of early-onset neonatal sepsis (within 72 hours of birth). It colonises the maternal genital tract and is transmitted during delivery. E. coli is the second most common cause. Listeria is a gram-positive rod (not coccus). Gram-positive diplococci on CSF smear = GBS until proven otherwise in a neonate. (Tintinalli's Emergency Medicine; Tietz Textbook of Laboratory Medicine)

Q2. A 2-year-old is brought in with sudden onset high fever, drooling, stridor, and the child is sitting forward in the "tripod" position, refusing to lie down. What was the historically classic causative organism, and how has its incidence changed?

A) Streptococcus pneumoniae - unchanged incidence
B) Staphylococcus aureus - rising incidence
C) Haemophilus influenzae type b (Hib) - dramatically decreased since vaccination
D) Parainfluenza virus - unchanged incidence

Answer: C Explanation: This is acute epiglottitis (supraglottitis). The classic tripod posturing, drooling, and stridor describe the "3 D's" - dysphagia, drooling, distress. Hib accounted for ~90% of paediatric epiglottitis cases before vaccination. Post-Hib vaccine, incidence has fallen markedly and Staphylococcus aureus / streptococcal organisms now predominate. Do NOT attempt to examine the throat - risk of complete obstruction. (Scott-Brown's Otorhinolaryngology; Barash Clinical Anesthesia)

Q3. A 6-week-old infant presents with a 2-week history of paroxysmal coughing episodes ending in a characteristic inspiratory "whoop," followed by post-tussive vomiting. There is lymphocytosis on FBC. What is the causative organism and its gram stain appearance?

A) Mycoplasma pneumoniae - no cell wall
B) Streptococcus pneumoniae - gram-positive diplococcus
C) Bordetella pertussis - gram-negative pleomorphic coccobacillus
D) Moraxella catarrhalis - gram-negative diplococcus

Answer: C Explanation: Whooping cough (pertussis) is caused by Bordetella pertussis, a gram-negative pleomorphic bacillus. It produces pertussis toxin and endotoxins that drive the characteristic paroxysmal cough. Lymphocytosis is a hallmark (pertussis toxin inhibits lymphocyte recirculation). The catarrhal phase (1-2 weeks) is the most infectious, followed by the paroxysmal phase. Diagnosis is by nasopharyngeal PCR or culture on Bordet-Gengou agar. Treatment: azithromycin. Vaccine: DTaP/Tdap. (Sherris & Ryan's Medical Microbiology; Scott-Brown's ORL)

Q4. Rotavirus is the most common cause of severe dehydrating diarrhoea in children under 5. Which of the following is CORRECT regarding rotavirus?

A) It is a DNA virus with a double-stranded capsid
B) Treatment is with oseltamivir
C) Oral rehydration therapy is the mainstay of treatment; antibiotics are not indicated
D) It predominantly affects children over 10 years

Answer: C Explanation: Rotavirus is a double-stranded RNA virus (Reoviridae family) with a triple-layered capsid - not DNA. It causes osmotic and secretory diarrhoea. ORT (oral rehydration therapy) is the cornerstone of management. Antibiotics and antivirals have no role in uncomplicated rotavirus gastroenteritis. Vaccination (Rotarix, RotaTeq) has dramatically reduced disease burden globally. (Park's Textbook of Preventive and Social Medicine)

Q5. A 7-year-old child develops a maculopapular rash starting on the face and spreading downward, preceded by Koplik's spots on the buccal mucosa, fever, cough, coryza and conjunctivitis ("the 3 C's"). Which statement is TRUE about the causative virus?

A) Caused by a DNA poxvirus
B) Transmitted by direct contact only
C) Caused by a paramyxovirus; spread by airborne route
D) Secondary attack rate in unvaccinated household contacts is approximately 30%

Answer: C Explanation: Measles (rubeola) is caused by a paramyxovirus (single-stranded, negative-sense RNA). It is one of the most contagious infectious diseases known, with a secondary attack rate of ~90% in susceptible household contacts (not 30%). Transmission is via airborne droplet nuclei that can remain infectious in air for up to 2 hours. Koplik's spots (white spots on red buccal mucosa) appear 1-2 days before the rash and are pathognomonic. Complications include pneumonia, encephalitis, and SSPE (subacute sclerosing panencephalitis).

Q6. A pregnant woman at 8 weeks gestation contracts a viral illness with a fine maculopapular rash and tender post-auricular lymphadenopathy. Her baby is born with cataracts, sensorineural deafness, and a patent ductus arteriosus. What is the diagnosis and the MOST common cardiac defect?

A) Congenital CMV - VSD
B) Congenital toxoplasmosis - ASD
C) Congenital Rubella Syndrome - Patent Ductus Arteriosus (PDA) and pulmonary artery stenosis
D) Congenital Zika - Tetralogy of Fallot

Answer: C Explanation: The classic triad of Congenital Rubella Syndrome (CRS) = cataracts + sensorineural deafness + cardiac defects (PDA and pulmonary valvular/artery stenosis are most common, followed by VSD). Risk is highest when infection occurs in the first trimester. Other features include microcephaly, "blueberry muffin" lesions (dermal erythropoiesis), hepatosplenomegaly, and developmental delay. Rubella is a togavirus. Prevention is with the MMR vaccine. (Creasy & Resnik's Maternal-Fetal Medicine; Sherris & Ryan's Medical Microbiology)

Q7. A 4-month-old infant is admitted with wheeze, tachypnoea, subcostal recessions and poor feeding. This is their first episode of wheeze. Chest X-ray shows hyperinflation. What is the MOST likely causative organism, and which treatment is NOT recommended?

A) Influenza A - oseltamivir not recommended
B) Mycoplasma pneumoniae - tetracycline not recommended
C) Respiratory Syncytial Virus (RSV) - corticosteroids are NOT recommended
D) Adenovirus - ribavirin not recommended

Answer: C Explanation: RSV is the leading cause of bronchiolitis in infants under 1 year. It is a paramyxovirus (negative-sense RNA). Key management points: supportive care with oxygen and hydration. Corticosteroids are NOT indicated (Cochrane reviews show no benefit). Bronchodilators are not routinely recommended. Antibiotics only if concurrent bacterial infection confirmed. Prophylaxis with palivizumab (anti-RSV monoclonal antibody) is used for high-risk infants (preterm, congenital heart disease). (Red Book 2021; Rosen's Emergency Medicine)

Q8. During an outbreak in a nursery school, a child develops a vesicular rash in different stages of healing simultaneously, affecting the trunk, scalp and face. The child had fever 1 day before the rash. What is the virus, its family, and the mechanism of latency?

A) Herpes simplex - Herpesviridae - latency in peripheral sensory ganglia via the same mechanism
B) Varicella-zoster virus (VZV) - Herpesviridae - establishes latency in dorsal root and cranial nerve ganglia
C) Molluscum contagiosum - Poxviridae - no true latency
D) Coxsackievirus A16 - Picornaviridae - no latency

Answer: B Explanation: Varicella (chickenpox) is caused by VZV, a double-stranded DNA virus of the Herpesviridae family. The hallmark is a pruritic vesicular rash in different stages simultaneously ("dewdrop on a rose petal"). VZV establishes latency in dorsal root ganglia (and cranial nerve ganglia), reactivating later in life as herpes zoster ("shingles"). Treatment in immunocompetent children is usually supportive; acyclovir for high-risk/immunocompromised. Secondary attack rate in susceptible household contacts ~90%.

Q9. A child with sickle cell disease develops acute bone pain crisis and aplastic crisis. Investigations show reticulocytopenia and the haemoglobin drops from 7 to 4 g/dL over 5 days. Which pathogen is responsible for the aplastic crisis?

A) Salmonella typhi
B) Parvovirus B19
C) Epstein-Barr virus (EBV)
D) Streptococcus pneumoniae

Answer: B Explanation: Parvovirus B19 is a single-stranded DNA virus that infects erythroid precursors (pronormoblasts) by binding the P antigen (globoside). In healthy children it causes "fifth disease" (erythema infectiosum - slapped cheek rash). In patients with high red cell turnover (sickle cell disease, hereditary spherocytosis, thalassaemia), it precipitates transient aplastic crisis with severe anaemia and reticulocytopenia. Treatment: red cell transfusion; IVIG in immunocompromised.

Q10. A 3-year-old child presents with high fever (>39°C), strawberry tongue, diffuse maculopapular rash sparing the palms and soles, pharyngitis and cervical lymphadenopathy. Throat culture grows beta-haemolytic gram-positive cocci in chains. What is the most feared complication if untreated?

A) Haemolytic uraemic syndrome
B) Thrombocytopenic purpura
C) Acute rheumatic fever (ARF) with carditis
D) Reactive arthritis (Reiter's syndrome)

Answer: C Explanation: This is scarlet fever caused by Streptococcus pyogenes (Group A Streptococcus, GAS) - gram-positive cocci in chains, beta-haemolytic. The rash is caused by erythrogenic (pyrogenic) exotoxins. The most feared non-suppurative complication of inadequately treated GAS pharyngitis is acute rheumatic fever, which can cause rheumatic heart disease (particularly mitral stenosis). HUS is associated with STEC (E. coli O157:H7) and rarely S. pneumoniae. Penicillin V is first-line treatment and prevents ARF.

Section B: Extended Matching Questions (EMQ)

Theme: Organisms causing paediatric meningitis by age group

Match each clinical scenario to the MOST likely causative organism:

Options:

A) Streptococcus agalactiae (GBS)
B) Neisseria meningitidis (serogroup B)
C) Listeria monocytogenes
D) Streptococcus pneumoniae
E) Haemophilus influenzae type b
F) Gram-negative enteric bacilli (E. coli)

Q11. A 2-day-old term neonate born by normal vaginal delivery; the mother was GBS screen positive but did not receive intrapartum antibiotics. The infant now has fever, lethargy and bulging fontanelle. CSF: gram-positive diplococci. Answer: A - GBS

Q12. A 6-week-old infant with meningitis; CSF shows gram-negative rods. Mother had a urinary tract infection during pregnancy. Answer: F - Gram-negative enteric bacilli (E. coli K1 capsular strain)

Q13. A 2-year-old presents with petechial/purpuric rash, high fever and meningism. She deteriorates rapidly within hours. Blood cultures requested urgently. Answer: B - Neisseria meningitidis (meningococcal septicaemia - a medical emergency; treat immediately with IV benzylpenicillin/cefotaxime without waiting for cultures)

Q14. A previously unvaccinated 65-year-old renal transplant patient develops meningitis with CSF showing gram-positive rods; ampicillin is added to cover this organism. Answer: C - Listeria monocytogenes (affects neonates, elderly, immunocompromised; resistant to cephalosporins - always add ampicillin)

Section C: True/False

Q15. Regarding congenital infections (TORCH):

Statement	T/F
A) CMV is the most common congenital viral infection worldwide	TRUE
B) Congenital toxoplasmosis classically shows intracranial calcifications in a periventricular distribution	FALSE (periventricular = CMV; toxoplasmosis = diffuse/scattered calcifications)
C) Congenital syphilis can present with "snuffles" (persistent rhinorrhoea) in the neonatal period	TRUE
D) Maternal primary HSV infection near delivery is more dangerous than recurrent infection	TRUE (higher viral load, no transplacental IgG yet)
E) Congenital rubella deafness is typically conductive	FALSE (sensorineural)

Q16. Regarding the MMR vaccine:

Statement	T/F
A) MMR is a live attenuated vaccine	TRUE
B) MMR can be given to a child with egg allergy	TRUE (MMR is grown on human diploid cells; minor egg allergy is not a contraindication)
C) MMR is contraindicated in HIV-positive children regardless of CD4 count	FALSE (can give if not severely immunocompromised, i.e., CD4 >15%)
D) A second dose of MMR is recommended to cover primary vaccine failures	TRUE

Section D: Short Answer / Data Interpretation

Q17. A CSF result shows: WBC 1200 cells/mm³ (90% neutrophils), glucose 1.5 mmol/L (serum glucose 5.8 mmol/L), protein 2.8 g/L. India ink stain is negative. Gram stain shows gram-positive diplococci.

(a) What is the diagnosis? (b) What CSF:serum glucose ratio indicates bacterial meningitis? (c) Name the first-line antibiotic and the adjunctive agent used to reduce neurological sequelae.

Answers:

(a) Bacterial (pneumococcal) meningitis
(b) CSF:serum glucose <0.4 (or CSF glucose <2.2 mmol/L absolute) suggests bacterial meningitis
(c) Ceftriaxone (third-generation cephalosporin) + dexamethasone (reduces risk of sensorineural hearing loss, particularly in H. influenzae and S. pneumoniae meningitis)

Q18. A 10-year-old child presents with bloody diarrhoea, oliguria and a platelet count of 28 x10⁹/L, Hb 6.5 g/dL (with fragmented red cells on smear), and creatinine 280 µmol/L.

(a) What is the diagnosis? (b) What is the causative organism and its virulence factor? (c) Why should antibiotics be AVOIDED?

Answers:

(a) Haemolytic uraemic syndrome (HUS) - the triad of microangiopathic haemolytic anaemia + thrombocytopaenia + acute kidney injury
(b) Enterohaemorrhagic Escherichia coli O157:H7 (EHEC/STEC); virulence factor = Shiga toxin (Stx1 and Stx2) which damages renal glomerular endothelial cells
(c) Antibiotics (especially fluoroquinolones) lyse the bacteria and trigger massive release of Shiga toxin, worsening renal injury and increasing HUS risk

Q19. Match the vaccine-preventable disease with its correct vaccine type:

Disease	Vaccine Type
Measles	Live attenuated
Pertussis	Acellular (killed component)
Hepatitis B	Recombinant subunit (HBsAg)
Meningococcal B	Protein-based (Bexsero)
Varicella	Live attenuated
H. influenzae type b	Conjugate polysaccharide

Q20. VIVA-style question: A 6-month-old is admitted with fever, bulging fontanelle, and a petechial rash. You suspect meningococcal disease.

(a) What is your immediate management (first 2 steps)? (b) What is the organism, its gram stain, and which serogroup is now most common in the UK post-MenC vaccination? (c) Which prophylaxis should be given to close household contacts, and why?

Answers:

(a) 1. IV/IO access + immediate IV benzylpenicillin (or cefotaxime) - do NOT delay antibiotics for LP. 2. Stabilise ABC, IV fluids, senior review/PICU referral
(b) Neisseria meningitidis - gram-negative diplococci (kidney/coffee bean shaped, intracellular in PMNs on smear). Serogroup B is now the most common in the UK (MenC vaccine has almost eliminated serogroup C)
(c) Rifampicin (or single-dose ciprofloxacin/ceftriaxone) for close contacts - to eradicate nasopharyngeal carriage and prevent secondary cases

Quick Reference: Key Paediatric Pathogens Summary

Age Group	Most Common Sepsis/Meningitis Organisms
0-3 months	GBS, E. coli, Listeria
3 months - 5 years	S. pneumoniae, N. meningitidis, (Hib if unvaccinated)
5-18 years	N. meningitidis, S. pneumoniae
Immunocompromised (any age)	Add: Listeria, fungi, Pseudomonas, CMV

Sources: Sherris & Ryan's Medical Microbiology 8e; Tintinalli's Emergency Medicine; Red Book 2021 (AAP); Creasy & Resnik's Maternal-Fetal Medicine; Scott-Brown's ORL; Rosen's Emergency Medicine; Park's Textbook of Preventive and Social Medicine

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