Infectious Diseases Practice Questions

Q: Koplik spots are pathognomonic of which of the following?

Measles. ***Measles*** - **Koplik spots** are small, white spots with a bluish-white center on an erythematous base, found on the buccal mucosa opposite the molars. - They are a **pathognomonic sign** of measles (rubeola) and typically appear 1-2 days before the generalized maculopapular rash. *Diphtheria* - Characterized by the formation of a **thick, grayish membrane (pseudomembrane)** in the throat and tonsils, which can cause respiratory obstruction. - It is caused by **_Corynebacterium diphtheriae_** and does not present with Koplik spots. *Donovanosis* - This is a chronic, progressive **genital ulcerative disease** caused by **_Klebsiella granulomatis_**. - It presents with **beefy-red, granulomatous lesions** on the genitals or perineum and has no association with oral lesions like Koplik spots. *Gonorrhea* - A **sexually transmitted infection** caused by **_Neisseria gonorrhoeae_**, primarily affecting the urethra, cervix, rectum, and pharynx. - Oral manifestations can include pharyngitis, but **Koplik spots are not a feature** of gonorrhea.

Q: Which of the following is the preferred treatment after birth for a baby of an HBsAg-positive mother?

HepB immunoglobulin + HepB immunization. ***HepB immunoglobulin + HepB immunization*** - This combination provides both **passive immunity** (immunoglobulin) and **active immunity** (immunization) to the newborn. - Administration within **12 hours of birth** is crucial to prevent perinatal transmission of hepatitis B from an HBsAg-positive mother. *HepB immunoglobulin only* - Provides only **temporary passive immunity** and does not induce long-lasting protection against hepatitis B. - While it offers immediate protection, it eventually wanes, leaving the infant susceptible without active immunization. *Only HepB immunization* - Induces **active immunity**, but it takes time to develop, leaving a window of vulnerability postpartum. - It would not provide immediate protection against the high risk of transmission from an HBsAg-positive mother. *No active treatment required* - This approach is incorrect and dangerous as infants of HBsAg-positive mothers are at a **very high risk of acquiring chronic hepatitis B infection**. - Without intervention, there is a **70-90% chance of developing chronic hepatitis B**, which can lead to serious liver disease later in life.

Q: An 8-year-old boy during a routine checkup is found to have E. coli 100,000 CFU/mL on a urine culture, obtained by mid-stream clean-catch void. The child is asymptomatic. Which is the most appropriate next step in the management?

No therapy. ***No therapy*** - The presence of **bacteria** in the urine (**bacteriuria**) without any accompanying symptoms like fever, dysuria, or flank pain is defined as **asymptomatic bacteriuria (ASB)**. - In healthy, asymptomatic children, ASB generally requires **no antibiotic treatment**, as it rarely progresses to symptomatic infection or causes renal damage and may even protect against symptomatic UTIs by competitive inhibition. *Treat as an acute episode of urinary tract infection* - This child is **asymptomatic,** therefore, he does not have an acute urinary tract infection (UTI). - Treating asymptomatic bacteriuria can lead to **antibiotic resistance** and unnecessary side effects without clinical benefit. *Prophylactic antibiotics for 6 months* - **Prophylactic antibiotics** are reserved for children with recurrent symptomatic UTIs or significant anatomical abnormalities like **vesicoureteral reflux (VUR)**, which are not indicated here. - Using long-term antibiotics in an asymptomatic child can contribute to the development of **antibiotic-resistant organisms**. *Administer long term urine alkalinizer* - **Urine alkalinizers** are used in specific conditions like certain types of **kidney stones (e.g., uric acid stones)** or to enhance the excretion of certain drugs, not for asymptomatic bacteriuria. - There is **no evidence** to support the use of urine alkalinizers in managing asymptomatic bacteriuria or preventing UTIs.

Q: Which of the following statements about chickenpox is false?

Crusts contain live varicella-zoster virus.. ***Crusts contain live varicella-zoster virus.*** - The **crusts** or scabs formed during chickenpox typically contain **inactive** or non-infectious viral particles. - The most infectious stages are the **macular, papular, and vesicular** lesions, before they crust over. *Rashes are pleomorphic.* - Chickenpox rash is **pleomorphic**, meaning various stages of lesions (macules, papules, vesicles, and crusts) can be seen simultaneously in the same body area. - This feature, often described as a **"dewdrop on a rose petal"** appearance, is characteristic of varicella. *Rashes are centripetal in distribution.* - The rash of chickenpox typically has a **centripetal distribution**, meaning it is more concentrated on the **trunk** and less so on the extremities. - This pattern helps differentiate it from other vesicular rashes. *Rapid progression from macule to vesicle is observed.* - Chickenpox lesions evolve quickly from a **macule** (flat red spot) to a **papule** (raised bump) and then into a characteristic **vesicle** (fluid-filled blister) within a few hours. - This rapid progression is a hallmark of the disease.

Q: An 8-year-old boy complains of left leg pain for 3 days. On physical examination, his temperature is 38.9°C, and he exhibits irritability when his left leg is moved. A radiograph of the left leg shows changes suggesting acute osteomyelitis in the proximal portion of the left femur. Culture of the infected bone is most likely to grow which of the following organisms?

Staphylococcus aureus. ***Staphylococcus aureus*** - **_Staphylococcus aureus_** is the most common cause of **acute osteomyelitis** in children. - The clinical presentation with a febrile child, localized leg pain, and radiographic changes strongly points to **bacterial osteomyelitis**, with **_S. aureus_** being the predominant pathogen. *Hemophilus influenzae* - **_Hemophilus influenzae_** was once a significant cause of osteomyelitis in children before widespread **HiB vaccination**. - Its incidence has drastically decreased, making it a less likely cause compared to **_S. aureus_** in an 8-year-old. *Neisseria gonorrhoeae* - **_Neisseria gonorrhoeae_** typically causes **septic arthritis** or osteomyelitis in sexually active adolescents and adults, often in disseminated infections. - It is an **uncommon cause** of osteomyelitis in an 8-year-old child and highly unlikely without a history of sexual abuse or neonatal exposure. *Salmonella enterica* - **_Salmonella enterica_** can cause osteomyelitis, particularly in patients with **sickle cell disease** or other **hemoglobinopathies**. - Without any mention of underlying predisposing conditions like sickle cell disease, **_Salmonella_** is a less probable cause than **_S. aureus_**.

Q: A child is brought to you because of perianal itching, which has been disturbing the child's sleep. Examination reveals scaly skin in the perianal region. You instruct the parents to place transparent tape on the perianal region the next morning, and then return to you. Next day, the tape is transferred to a microscope slide, and low-power examination of the tape reveals oval eggs that are flattened along one side. What is the most likely cause?

Enterobius vermicularis (pinworm). ***Enterobius vermicularis (pinworm)*** - The classic presentation of **perianal itching**, especially disrupting sleep, combined with the finding of **oval eggs flattened on one side** via the **tape test**, is pathognomonic for *Enterobius vermicularis* infection. - Female pinworms migrate to the **perianal region at night** to lay eggs, causing intense pruritus. *Ancylostoma duodenale (hookworm)* - Hookworm infections typically cause **gastrointestinal symptoms** and **iron-deficiency anemia**, not primarily perianal itching. - Hookworm eggs are usually **oval**, thin-shelled, and contain **developing larvae**, but are not flattened on one side and are found in stool samples, not perianal tape tests. *Ascaris lumbricoides (roundworm)* - *Ascaris lumbricoides* infection often presents with **gastrointestinal and pulmonary symptoms** (due to larval migration). - Its eggs are typically **mammillated** (roughened outer shell) or smooth (decorticated) and are detected in **stool samples**, not through a perianal tape test. *Necator americanus (hookworm)* - Similar to *Ancylostoma duodenale*, *Necator americanus* causes **anemia** and **gastrointestinal issues** and is acquired through skin penetration. - Its eggs are morphologically similar to *Ancylostoma duodenale* eggs (thin-shelled, containing developing larvae), found in **stool**, and do not cause perianal itching or show the flattened morphology seen in pinworm.

Q: An infant presenting with itchy lesions over the groin and prepuce, all of the following are indicated except:

Dispose of all clothes by burning. ***Dispose of all clothes by burning*** - While **scabies mites** can survive off-host for a limited time, disposal of all clothes by burning is an **extreme and unnecessary measure**. - Proper laundering of clothes and linens in hot water, followed by hot drying, is sufficient to kill mites and prevent reinfestation. *Bath & apply scabicidal solution* - A bath helps to clean the skin before applying a **scabicidal solution**, which is the primary treatment for eradicating **scabies mites**. - The solution, usually permethrin cream, needs to be applied to the entire body (neck down) and left on for the recommended time to be effective. *Treatment of all family members* - **Scabies** is highly contagious, and asymptomatic family members can be carriers and a source of reinfestation for the infant. - Treating all close contacts, even if they show no symptoms, is crucial to prevent the spread and recurrence of the infestation. *IV antibiotics* - **Scabies** is caused by a mite infestation, not a bacterial infection, so **antibiotics are not indicated** for treating the scabies itself. - **IV antibiotics** would only be considered if there were a **secondary bacterial skin infection** (e.g., impetigo) that was severe enough to warrant intravenous administration.

Q: All of the following are contraindications to the pertussis-containing vaccine except which of the following?

No known allergies. ***No known allergies*** - The absence of known allergies is **not a contraindication** to vaccination; rather, it suggests an individual is less likely to experience an **allergic reaction**. - This option describes a **normal and healthy** patient profile, suitable for vaccination. *Uncontrolled epilepsy* - **Uncontrolled epilepsy** represents an **unstable neurological condition** and is a **contraindication** to pertussis vaccination per current guidelines. - Progressive or unstable neurological disorders are contraindications because vaccination might be **temporally associated** with neurological deterioration, making it difficult to determine causality. - Once epilepsy is **controlled and stable**, pertussis vaccination may be reconsidered. *Anaphylactic reaction to previous dose* - A confirmed **anaphylactic reaction** to a prior dose of any vaccine component is an **absolute contraindication** to further doses. - Re-exposure could lead to a **severe and life-threatening** allergic response. *Progressive encephalopathy* - **Progressive encephalopathy** without an identified cause occurring within 7 days after a previous dose of pertussis vaccine is an **absolute contraindication**. - Vaccination in this context could exacerbate the condition or confuse the diagnosis of the underlying encephalopathy.

Q: What is the most common cause of acute epiglottitis in children in the post-Hib vaccination era?

Streptococcus pyogenes (Group A Strep). ***Streptococcus pyogenes (Group A Strep)*** - In the **post-Hib vaccination era**, *Streptococcus pyogenes* has emerged as **one of the most common causes** of acute epiglottitis in children. - With the dramatic reduction in H. influenzae type B cases due to widespread vaccination, Group A Streptococcus now accounts for a significant proportion of bacterial epiglottitis cases. - Other common causes in the current era include *Streptococcus pneumoniae* and *Staphylococcus aureus*. *Hemophilus influenzae type B* - While H. influenzae type B was the **predominant cause in the pre-vaccination era**, its incidence has **declined by over 95%** since the introduction of the Hib vaccine. - Cases now occur primarily in **unvaccinated or incompletely vaccinated children** and are relatively rare in populations with high vaccination coverage. - The question specifically asks about the post-Hib vaccination era, making this no longer the most common cause. *Para influenza virus type I and II* - **Parainfluenza viruses**, particularly types I and II, are the **leading cause of croup** (laryngotracheobronchitis), not epiglottitis. - Croup primarily affects the **subglottic region** and presents with a characteristic **barking cough**, whereas epiglottitis involves the supraglottic structures and presents with drooling, dysphagia, and the "tripod position." *Streptococcus pneumoniae* - *Streptococcus pneumoniae* is also a **common cause of acute epiglottitis in the post-Hib era**, along with Group A Streptococcus. - While S. pneumoniae can cause epiglottitis, Group A Strep is generally cited more frequently in recent literature as a leading bacterial cause in the current era. - Both organisms have become more prominent as etiologic agents following the decline of H. influenzae type B.

Question 1

Koplik spots are pathognomonic of which of the following?

Accepted Answer

Measles

Answer

Diphtheria

Answer

Donovanosis

Answer

Gonorrhoea

Question 2

Which of the following is the preferred treatment after birth for a baby of an HBsAg-positive mother?

Accepted Answer

HepB immunoglobulin + HepB immunization

Answer

HepB immunoglobulin only

Answer

Only HepB immunization

Answer

No active treatment required

Question 3

A 12-year-old child presents with 4 lesions of leprosy on their back and four lesions on their left arm. What should be the treatment for this child?

Accepted Answer

Rifampicin 450 mg once monthly + Dapsone 50 mg daily + Clofazimine 50 mg alternate day

Answer

Rifampicin 300 mg once monthly + Dapsone 25 mg daily

Answer

Rifampicin 450 mg once monthly + Dapsone 50 mg daily

Answer

Rifampicin 600 mg once monthly + Dapsone 100 mg daily

Question 4

An 8-year-old boy during a routine checkup is found to have E. coli 100,000 CFU/mL on a urine culture, obtained by mid-stream clean-catch void. The child is asymptomatic. Which is the most appropriate next step in the management?

Accepted Answer

No therapy

Answer

Prophylactic antibiotics for 6 months

Answer

Administer long term urine alkalinizer

Answer

Treat as an acute episode of urinary tract infection

Question 5

Which of the following statements about chickenpox is false?

Accepted Answer

Crusts contain live varicella-zoster virus.

Answer

Rashes are centripetal in distribution.

Answer

Rashes are pleomorphic.

Answer

Rapid progression from macule to vesicle is observed.

Question 6

An 8-year-old boy complains of left leg pain for 3 days. On physical examination, his temperature is 38.9°C, and he exhibits irritability when his left leg is moved. A radiograph of the left leg shows changes suggesting acute osteomyelitis in the proximal portion of the left femur. Culture of the infected bone is most likely to grow which of the following organisms?

Accepted Answer

Staphylococcus aureus

Answer

Hemophilus influenzae

Answer

Neisseria gonorrhoeae

Answer

Salmonella enterica

Question 7

A child is brought to you because of perianal itching, which has been disturbing the child's sleep. Examination reveals scaly skin in the perianal region. You instruct the parents to place transparent tape on the perianal region the next morning, and then return to you. Next day, the tape is transferred to a microscope slide, and low-power examination of the tape reveals oval eggs that are flattened along one side. What is the most likely cause?

Accepted Answer

Enterobius vermicularis (pinworm)

Answer

Ancylostoma duodenale (hookworm)

Answer

Ascaris lumbricoides (roundworm)

Answer

Necator americanus (hookworm)

Question 8

An infant presenting with itchy lesions over the groin and prepuce, all of the following are indicated except:

Accepted Answer

Dispose of all clothes by burning

Answer

IV antibiotics

Answer

Treatment of all family members

Answer

Bath & apply scabicidal solution

Question 9

All of the following are contraindications to the pertussis-containing vaccine except which of the following?

Accepted Answer

No known allergies

Answer

Uncontrolled epilepsy

Answer

Anaphylactic reaction to previous dose

Answer

Progressive encephalopathy

Question 10

What is the most common cause of acute epiglottitis in children in the post-Hib vaccination era?

Accepted Answer

Streptococcus pyogenes (Group A Strep)

Answer

Hemophilus influenzae type B

Answer

Para influenza virus type I and II

Answer

Streptococcus pneumoniae

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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