Common Infections

Common Infections UK Medical PG Question 1: A 65-year-old man with diabetes presents with a non-healing foot ulcer for 3 months. X-ray shows osteolytic changes in the underlying bone. MRI confirms osteomyelitis. What is the most appropriate treatment duration for antibiotics?

• A. 2 weeks IV
• B. 4 weeks IV
• C. 6 weeks IV
• D. 4-6 weeks IV followed by 2-6 weeks oral
• E. 12 weeks total therapy (Correct Answer)

Common Infections Explanation: ***12 weeks total therapy***- The treatment duration for confirmed **diabetic foot osteomyelitis (DFO)** without amputation or with residual infected bone often requires 10–12 weeks or 3 months of total antibiotic therapy (IV and/or oral) to achieve cure and prevent relapse.- Prolonged treatment is crucial because of the **poor vascular supply** in diabetic feet and the low penetration of antibiotics into the avascular, infected bone. *2 weeks IV*- This duration is insufficient for bone infection, as antibiotics require extended time to reach therapeutic concentrations within the **avascular, necrotic bone**.- **Acute uncomplicated cellulitis** or soft tissue infection might be treated in 2 weeks, but not osteomyelitis. *4 weeks IV*- A 4-week course might be considered sufficient only if the infected bone has been completely removed during **surgical debridement** (e.g., partial foot amputation), which is not guaranteed by the prompt.- This duration drastically increases the risk of **relapse** in confirmed, non-surgically cleared osteomyelitis. *6 weeks IV*- This is the standard duration for **vertebral osteomyelitis** or chronic osteomyelitis where adequate surgical debridement was achieved, often substituting for the total 12-week regimen.- However, for conservative management of **DFO**, guidelines often recommend a total of 10–12 weeks (IV and oral) to maximize bone penetration. *4-6 weeks IV followed by 2-6 weeks oral*- While this combination (totaling 6–12 weeks) is a common strategy, it is less definitive than the 12-week option and can be interpreted as potentially insufficient depending on the chosen duration (e.g., 6 weeks total is too short).- The **IDSA guidelines** often suggest at least 6 weeks following resection of infected bone, but up to 12 weeks is recommended if bone cannot be fully resected or infection is severe.

Common Infections UK Medical PG Question 2: A 16-year-old boy presents with a 1-week history of sore throat and fever. He has developed a widespread maculopapular rash after taking amoxicillin prescribed by his GP. What is the most likely underlying diagnosis?

• A. Penicillin allergy
• B. Infectious mononucleosis (Correct Answer)
• C. Scarlet fever
• D. Kawasaki disease
• E. Stevens-Johnson syndrome

Common Infections Explanation: ***Infectious mononucleosis***- The classic triad of **fever**, **pharyngitis** (sore throat), and **lymphadenopathy** in a young patient is highly suggestive of infectious mononucleosis, commonly caused by **Epstein-Barr virus (EBV)**.- A **widespread maculopapular rash** following amoxicillin administration is a very common and characteristic reaction in patients with infectious mononucleosis, often misinterpreted as a penicillin allergy.*Penicillin allergy*- While a rash after amoxicillin can indicate a penicillin allergy, the preceding symptoms of **sore throat and fever** for a week make an underlying infection, specifically mononucleosis, a more likely cause for the rash.- True penicillin allergies often present with **urticaria**, angioedema, or anaphylaxis, rather than a widespread maculopapular rash exacerbated by a viral illness.*Scarlet fever*- Scarlet fever is caused by **Streptococcus pyogenes** and presents with a characteristic **sandpaper-like rash** (finely papular, erythematous) and **strawberry tongue**, which are not described here.- While it causes sore throat and fever, the rash associated with scarlet fever is distinct from a generalized maculopapular rash triggered by amoxicillin in the context of mononucleosis.*Kawasaki disease*- Kawasaki disease primarily affects **young children** (typically under 5 years old) and is characterized by prolonged fever, **conjunctival injection**, **mucosal changes** (strawberry tongue, red lips), **polymorphous rash**, **cervical lymphadenopathy**, and **extremity changes**.- The patient's age (16 years old) and the specific rash reaction to amoxicillin make Kawasaki disease highly unlikely.*Stevens-Johnson syndrome*- **Stevens-Johnson syndrome (SJS)** is a severe mucocutaneous reaction, often drug-induced, characterized by widespread **bullae**, **erosions**, and **mucosal involvement** (oral, ocular, genital) with significant skin detachment (less than 10% total body surface area).- The description of a **widespread maculopapular rash** in this case is not consistent with the severe blistering and erosions typical of SJS.

Common Infections UK Medical PG Question 3: A 35-year-old man with HIV infection (CD4 count 80 cells/mm³, viral load 125,000 copies/mL, not on antiretroviral therapy) presents with a 4-week history of headache, fever, and confusion. CT head shows basal meningeal enhancement and multiple small nodules. Lumbar puncture shows: opening pressure 32 cmH2O, CSF white cells 45/mm³ (80% lymphocytes), protein 1.2 g/L, glucose 1.9 mmol/L (serum glucose 5.4 mmol/L). India ink stain is positive. Cryptococcal antigen is positive in both CSF and serum at titres of 1:2048 and 1:1024 respectively. He is started on liposomal amphotericin B and flucytosine. Which one of the following additional interventions has been shown to improve survival in this patient?

• A. Commencing antiretroviral therapy immediately alongside antifungal treatment
• B. Adding adjunctive dexamethasone 0.4 mg/kg daily for 6 weeks
• C. Performing daily therapeutic lumbar punctures until opening pressure normalizes (Correct Answer)
• D. Adding adjunctive interferon-gamma to enhance immune response
• E. Inserting a ventriculoperitoneal shunt to manage hydrocephalus

Common Infections Explanation: ***Performing daily therapeutic lumbar punctures until opening pressure normalizes*** - Management of **elevated intracranial pressure** (opening pressure >25 cmH2O) is critical, as it is a major cause of mortality in **cryptococcal meningitis** associated with HIV. - Daily drainage of 20-30 mL of CSF is recommended to achieve an **opening pressure** of <20 cmH2O or a 50% reduction from baseline, which significantly **improves survival** and reduces neurological sequelae. *Commencing antiretroviral therapy immediately alongside antifungal treatment* - **Early initiation of ART** (within 2 weeks) in HIV-associated cryptococcal meningitis is associated with an increased risk of **Immune Reconstitution Inflammatory Syndrome (IRIS)** and higher mortality. - Current guidelines recommend deferring ART for **4 to 6 weeks** after the initiation of induction antifungal therapy to allow for partial clearance of the fungal load and reduce IRIS risk. *Adding adjunctive dexamethasone 0.4 mg/kg daily for 6 weeks* - Routine use of **corticosteroids** is contraindicated in cryptococcal meningitis as they have been shown to **increase mortality** and reduce fungal clearance rates in clinical trials. - Steroids also increase the risk of serious **adverse events** without providing any survival benefit in these patients. *Adding adjunctive interferon-gamma to enhance immune response* - While **interferon-gamma** may facilitate faster fungal clearance in some experimental settings, it has not been shown to provide a **survival benefit** in high-quality clinical trials for HIV-associated cryptococcal meningitis. - It is not currently recommended as part of the **standard induction therapy** for this condition. *Inserting a ventriculoperitoneal shunt to manage hydrocephalus* - **Ventriculoperitoneal (VP) shunts** are generally reserved for patients who fail to respond to repeated **therapeutic lumbar punctures** or develop persistent symptomatic hydrocephalus refractory to medical management. - Although useful for long-term pressure management, it is not the primary or first-line intervention for improving **acute survival** compared to serial lumbar punctures, which are less invasive and carry fewer immediate risks.

Common Infections UK Medical PG Question 4: A 25-year-old woman presents with a 2-week history of sore throat, fever, and fatigue. She has cervical lymphadenopathy and splenomegaly. Her throat swab is negative for Group A Streptococcus. What is the most likely diagnosis?

• A. Viral pharyngitis
• B. Infectious mononucleosis (Correct Answer)
• C. Bacterial pharyngitis
• D. Diphtheria
• E. Candidiasis

Common Infections Explanation: ***Infectious mononucleosis***- The constellation of prolonged **fever**, **pharyngitis**, diffuse **lymphadenopathy**, and **splenomegaly** in a young adult is the classic presentation of primary infection with **Epstein-Barr Virus (EBV)**.- The relatively long duration of symptoms (2 weeks), the presence of **splenomegaly**, and the **negative Group A Strep swab** strongly suggest infectious mononucleosis.*Viral pharyngitis*- Common viral causes (e.g., rhinovirus, adenovirus) usually result in an acute illness, lasting less than 10 days, and do not typically cause sustained systemic symptoms or significant **splenomegaly**.- While presenting with sore throat and fever, non-EBV viral pharyngitis lacks the profound, persistent **fatigue** and notable **lymphadenopathy** seen in infectious mononucleosis.*Bacterial pharyngitis*- This is typically caused by *Streptococcus pyogenes* (Group A Strep), which was **ruled out by the negative throat swab**.- **Bacterial pharyngitis** rarely causes the sustained constitutional symptoms and concurrent **splenomegaly** seen in this case.*Diphtheria*- The hallmark of **diphtheria** is the presence of a thick, adherent, gray-white **pseudomembrane** on the tonsils and pharynx, which is not described in this patient.- It is rare in vaccinated populations and often leads to severe systemic toxicity (e.g., **myocarditis**) rather than the classic infectious mononucleosis triad.*Candidiasis*- Pharyngeal **candidiasis (thrush)** presents as white, easily removable plaques, often favored by antibiotic use or **immunosuppression**.- It is primarily a localized mucosal infection and usually does not cause the fever, systemic illness, or **splenomegaly** seen here.

Common Infections UK Medical PG Question 5: A 31-year-old man presents with fever, sore throat, and a widespread maculopapular rash after taking amoxicillin prescribed by his GP. What is the most likely underlying diagnosis?

• A. Penicillin allergy
• B. Infectious mononucleosis (Correct Answer)
• C. Scarlet fever
• D. Kawasaki disease
• E. Stevens-Johnson syndrome

Common Infections Explanation: ***Infectious mononucleosis*** - The combination of **fever**, **sore throat**, and a widespread **maculopapular rash** after taking amoxicillin is a classic presentation for **Epstein-Barr virus (EBV)** infection (infectious mononucleosis). - Approximately 80-90% of patients with infectious mononucleosis develop a non-allergic, diffuse rash when treated with **amoxicillin** or **ampicillin**. *Penicillin allergy* - A true **penicillin allergy** (Type I hypersensitivity) typically manifests as rapid onset **urticaria**, angioedema, or anaphylaxis, or a delayed itchy morbilliform rash, usually without the characteristic mononucleosis triad of symptoms. - The rash in mononucleosis patients taking amoxicillin is a **pharmacological interaction** with the underlying viral process, not a typical immunological allergic reaction. *Scarlet fever* - Characterized by a **sandpaper-like erythrodermic rash** and **circumoral pallor**, caused by *Streptococcus pyogenes* erythrogenic toxins. - The current presentation with a maculopapular rash specifically after amoxicillin is not typical of a streptococcal rash and strongly points towards a viral etiology. *Kawasaki disease* - This is a **medium-vessel vasculitis** primarily affecting **children** (typically under 5 years old), making it a highly unlikely diagnosis in a 31-year-old man. - Diagnosis requires persistent fever plus specific criteria like conjunctivitis, oral changes, peripheral extremity changes, lymphadenopathy, and a polymorphous rash. *Stevens-Johnson syndrome* - SJS is a severe, life-threatening **mucocutaneous reaction** characterized by **atypical target lesions** and prominent involvement of **mucous membranes** (oral, ocular, genital). - This condition involves significant **epidermal detachment** (less than 10% of total body surface area) and is distinct from a simple widespread maculopapular rash.

Common Infections Flashcard 1 of 5

Question: Recurrent vulvovaginal candidiasis should be investigated for _____

Answer: diabetes mellitus

Common Infections Flashcard 2 of 5

Question: Most common causes of osteomyelitis: Overall: _____ Diabetes: Polymicrobial Penetrative puncture: Pseudomonas aeruginosa Sickle cell: Salmonella > Staph aureus

Answer: Staphylococcus aureus

Common Infections Flashcard 3 of 5

Question: _____ are infections occuring ≥ 48 hours after admission, not present or incubating at the time of hospital entry

Answer: Hospital-acquired infections

Common Infections Flashcard 4 of 5

Question: "_____" gangrene is caused by bacterial superinfection

Answer: Wet

Common Infections Flashcard 5 of 5

Question: Asymptomatic/mild COVID-19 can be managed _____

Answer: at home