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 a 2-week history of **sore throat**, **fever**, profound **fatigue**, widespread **cervical lymphadenopathy**, and **splenomegaly** in a young adult is the classic presentation of infectious mononucleosis, primarily caused by **Epstein-Barr Virus (EBV)**.- The **negative throat swab for Group A Streptococcus** further supports a non-bacterial cause, and the prolonged symptoms with significant systemic involvement are key indicators.*Viral pharyngitis*- Typical **viral pharyngitis** is generally milder, resolves more quickly (within 3-5 days), and does not typically cause the significant systemic features such as profound **fatigue** and **splenomegaly** described.- While lymphadenopathy can occur, it is usually less generalized and prominent compared to the widespread involvement seen here.*Bacterial pharyngitis*- The patient's **negative throat swab for Group A Streptococcus** effectively rules out the most common bacterial cause of pharyngitis (strep throat).- Bacterial pharyngitis usually has a more acute onset, a shorter course, and rarely involves systemic findings like significant **fatigue** or **splenomegaly**.*Diphtheria*- **Diphtheria** is primarily characterized by the formation of a thick, adherent, **grayish-white pseudomembrane** over the tonsils and pharynx, which is not mentioned in the patient's presentation.- Although it can cause pharyngitis and fever, the combination of **splenomegaly** and diffuse, persistent lymphadenopathy is not typical for diphtheria.*Candidiasis*- **Oral candidiasis** (thrush) typically presents with creamy **white plaques** on the oral mucosa that can be scraped off, usually in immunocompromised individuals.- This is a localized fungal infection and would not cause the systemic findings of high fever, widespread lymphadenopathy, and **splenomegaly**.

Common Infections UK Medical PG Question 5: 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 6: 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 UK Medical PG Question 7: A 58-year-old man with diabetes presents with severe foot pain and a deep ulcer exposing bone. X-ray shows osteolytic changes. What is the most likely complication?

• A. Cellulitis
• B. Osteomyelitis (Correct Answer)
• C. Charcot arthropathy
• D. Peripheral arterial disease
• E. Deep vein thrombosis

Common Infections Explanation: ***Osteomyelitis***- The patient's presentation of a **deep ulcer exposing bone** in the setting of **diabetes**, coupled with **severe foot pain** and **osteolytic changes** on X-ray, are classic indicators of osteomyelitis (bone infection).- **Diabetic foot ulcers** provide a direct pathway for bacterial invasion into the underlying bone, leading to destructive changes visible on imaging like X-rays.*Cellulitis*- Cellulitis is a bacterial infection of the **superficial skin and subcutaneous tissue**, characterized by **erythema**, warmth, and localized swelling.- It typically does not involve the underlying bone and therefore would not present with **bone exposure** or **osteolytic changes** on X-ray.*Charcot arthropathy*- **Charcot arthropathy** is a neuropathic joint degeneration, commonly seen in advanced diabetes, causing progressive joint destruction and deformity, often a **"rocker-bottom" foot**.- While it can lead to foot deformity and subsequent ulceration, it is typically **painless** due to significant neuropathy, contrasting with the patient's **severe pain**, and direct osteolytic changes of infection are not its primary X-ray feature.*Peripheral arterial disease*- **Peripheral arterial disease (PAD)** causes reduced blood flow to the extremities, leading to symptoms like **claudication**, **ischemic ulcers** (often on toes/heels), and rest pain.- While a significant comorbidity in diabetics and a risk factor for ulcers, PAD primarily involves vascular insufficiency and does not directly cause the **osteolytic changes** indicative of bone infection.*Deep vein thrombosis*- **Deep vein thrombosis (DVT)** is a blood clot in a deep vein, typically presenting as **unilateral leg swelling**, pain, and warmth.- It is a vascular issue not primarily associated with ulcers exposing bone, nor does it cause the **osteolytic changes** on a foot X-ray.

Common Infections UK Medical PG Question 8: A 34-year-old woman with Crohn's disease on adalimumab presents with a 10-day history of multiple painful nodules on both shins. The lesions are 2-4cm in diameter, raised, tender, and erythematous without ulceration or pustulation. She reports associated joint pains in her knees and ankles but no fever. Recent colonoscopy showed active inflammation. Blood tests reveal WCC 11.2 × 10⁹/L, CRP 78 mg/L, ESR 65 mm/hr. What is the most likely diagnosis?

• A. Cellulitis secondary to immunosuppression
• B. Pyoderma gangrenosum
• C. Erythema nodosum (Correct Answer)
• D. Sweet's syndrome (acute febrile neutrophilic dermatosis)
• E. Subcutaneous nodular panniculitis from adalimumab injection sites

Common Infections Explanation: ***Erythema nodosum*** - This patient presents with classic **tender, erythematous nodules** on the **shins** and associated **arthralgia** in the knees and ankles, which is a common extraintestinal manifestation of **Crohn's disease**. - The active intestinal inflammation noted on colonoscopy and elevated **CRP** and **ESR** correlate well with the onset of erythema nodosum, which often reflects underlying disease activity. *Cellulitis secondary to immunosuppression* - Typically presents as a **unilateral**, diffuse area of skin erythema and warmth, often with a spreading border, rather than discrete, **bilateral nodules**. - Usually accompanied by systemic features such as **fever** and significant pain upon touch, which are not explicitly reported here as the primary presenting features. *Pyoderma gangrenosum* - Characterized by rapidly enlarging, **painful ulcers** with **undermined violaceous borders** and purulent bases, whereas this patient has non-ulcerated nodules. - While also associated with **Inflammatory Bowel Disease (IBD)**, its distinctive ulcerative morphology is a key differentiator from the patient's presentation. *Sweet's syndrome (acute febrile neutrophilic dermatosis)* - Typically presents with the sudden onset of painful, edematous, **erythematous plaques** or nodules frequently associated with a **high fever** and marked **peripheral neutrophilia**. - The absence of fever and the nodular presentation without prominent plaques make this diagnosis less likely compared to erythema nodosum. *Subcutaneous nodular panniculitis from adalimumab injection sites* - These reactions would be localized strictly to the **site of injection**, commonly the **abdomen or thighs**, and would not typically manifest as widespread bilateral shin nodules. - Such reactions are usually local inflammatory responses and not typically indicative of a systemic flare-up of Crohn's disease with corresponding elevated inflammatory markers like **CRP** and **ESR**.

Common Infections UK Medical PG Question 9: A 72-year-old man with chronic obstructive pulmonary disease is admitted with an exacerbation and started on prednisolone 30mg daily. On day 3 of admission, he develops a painful, erythematous rash on his right shin. The affected area is warm and tender with a well-demarcated, raised border and has a characteristic orange-peel (peau d'orange) appearance. His temperature is 38.4°C. Blood tests show WCC 16.2 × 10⁹/L, CRP 128 mg/L. Which organism is most likely responsible for this infection?

• A. Staphylococcus aureus
• B. Streptococcus pyogenes (Group A Streptococcus) (Correct Answer)
• C. Pseudomonas aeruginosa
• D. Haemophilus influenzae
• E. Pasteurella multocida

Common Infections Explanation: ***Streptococcus pyogenes (Group A Streptococcus)***- This patient presents with **erysipelas**, a superficial skin infection most commonly caused by **Group A Streptococcus**.- Characteristic features include a **well-demarcated**, raised border and a **peau d'orange** appearance due to involvement of the superficial lymphatics.*Staphylococcus aureus*- More commonly associated with **cellulitis**, which involves deeper dermis and subcutaneous fat with less defined borders.- Often linked to **purulent infections** and abscess formation, rather than the clear-cut edges seen here.*Pseudomonas aeruginosa*- Typically associated with **hot tub folliculitis** or infections following exposure to **contaminated water/moist environments**.- Usually presents in **immunocompromised patients** as ecthyma gangrenosum, which features necrotic ulcers rather than orange-peel skin.*Haemophilus influenzae*- A rare cause of skin infections in adults, occasionally causing facial cellulitis in **unvaccinated children**.- Clinical presentation usually lacks the specific **well-demarcated raised border** seen in this patient’s shin lesion.*Pasteurella multocida*- Primarily associated with cellulitis following **animal bites or scratches**, particularly from **cats or dogs**.- Onset is typically very rapid (within 24 hours of a bite), which does not correlate with this hospital-acquired presentation.

Common Infections Flashcard 1 of 10

Question: Recurrent vulvovaginal candidiasis should be investigated for _____

Answer: diabetes mellitus

Common Infections Flashcard 2 of 10

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 10

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 10

Question: "_____" gangrene is caused by bacterial superinfection

Answer: Wet

Common Infections Flashcard 5 of 10

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

Answer: at home

Common Infections Flashcard 6 of 10

Question: Hospital-acquired infections can involve _____-resistant organisms

Answer: multidrug

Common Infections Flashcard 7 of 10

Question: A false +ve RPR or VDRL can be caused by _____, pregnancy, or autoimmune diseases (e.g. SLE, APS)

Answer: infections

Common Infections Flashcard 8 of 10

Question: Overestimation of oxygen saturations using a pulse oximeter has been documented in _____

Answer: individuals with darker skin

Common Infections Flashcard 9 of 10

Question: A -ve EIA or TPPA indicates _____ or very early infection (false -ve)

Answer: absent current or past infection

Common Infections Flashcard 10 of 10

Question: _____ infections are the most common hospital-acquired infections

Answer: Respiratory