Infectious Diseases Flashcards
Definition of pneumonia
Infection of lung tissue causing inflammation and sputum filling the airways and alveoli.
What are the types of pneumonia
- Community Acquired Pneumonia (CAP)
- Hospital Acquired Pneumonia (HAP)
- Aspiration pneumonia
- Atypical pneumonia
Symptoms of pneumonia
- SOB
- cough with purulent sputum
- fever
- haemoptysis
- pleuritic chest pain
- delirum
- sepsis
Signs of pneumonia
Characteristic chest signs
* bronchial breath sounds = harsh breath sounds due to consolidation
* focal coarse crackles = air passing through sputum
* dullness to percussion - lung collapse &/or consolidation
Sepsis secondary to pneumonia
* tachypnoea
* tachycardia
* hypoxia
* hypotension
How is the severity of pneumonia assessed?
CURB-65 (CRB-65 out of hospital)
* Confusion: abbreviated mental test ≤8 or disorientated
* Urea >7
* RR ≥ 30
* BP: SBP <90 or DBP ≤60
* Age ≥65
0-1 = mild, consider treatment at home
≥2 = moderate, consider hospitalisation
≥3 = severe, consider intensive care assessment
Common bacterial causes of pneumonia
- streptococcus pneumoniae (50%)
- haemophilus influenzae (20%)
Other bacterial causes and associations of pneumonia
- moraxella catarrhalis in the immunocompromised or chronic pulmonary disease
- pseudomonas aeruginosa in patients with cystic fibrosis or bronchiectasis
- staphylococcus aureus in patients with cystic fibrosis
Causes of atypical pneumonia
Mycoplasma pneumoniae
* can cause rash = erythema multiforme (pink ring, pale centre)
* can cause neurological symptoms
Chlamydophila pneumoniae = mild to moderate chronic pneumonia and wheeze
Coxiella burnetii = typically contracted from contact with infected birds
Legionella pneumophila
* caused by infected water supplies or air conditioning units
* Can cause SIADH = hyponatraemia
Investigations for pneumonia
- Basic Obs
- CXR
- Bloods: FBC, U+E, LFT, CRP, blood culture
- Sputum culture
- O2 sats, ABG if <92% or severely unwell
Abx for CAP
- Mild-moderate: amoxicillin PO. Clarithromycin or doxycycline if allergic.
- Severe: co-amoxiclav, cefuroxime, or cefotaxime IV (or levofloxacin if allergic), plus clarithromycin IV
- If hospitalised, start within 4 hrs. Monitor response to treatment with CRP
Abx for HAP
- Piperacilin/tazobactam, 3rd generation cephalosporin, meropenem, or levofloxacin IV.
- Co-amoxiclav is a PO alternative or stepdown
- Add vancomycin or teicoplanin or linezolid if MRSA suspected
Abx for aspiration pneumonia
clindamycin, levofloxacin, or piperacilin/tazobactam
Duration of abx in pneumonia
- 5 days total usually sufficient
- longer if remains febrile or unstable, or for certain pathogens e.g. pseudomonas
- If starting IV, review after 48 hrs for possible PO stepdown
Supportive care in pneumonia
- oxygen
- fluids
- paracetamol
Prognosis of pneumonia
- fever should resolve within 1 week
- cough and SOB may take up to 6 weeks to resolve
- fatigue may persist up to 3 months
Complications of pneumonia
- Respiratoy failure
- sepsis and septic shock
- uncomplicated parapneumonic pleural effusion, empyema, or lung abscess
- Death: 1% in community, 10% if admitted
Pathophysiology of infective endocarditis
- infection of the endocardium, usually a (prosthetic or native) valve (mitral or aortic), usually following transient bacteraemia and turbulent flow past valve
- leads to formation of vegetation on valves containing bacteria, fibrin and platelets
Causes of infective endocarditis
- bacterial: strep viridans, staph aureus
- fungal: candida, aspergillus
- non-infective: cancer, SLE
Key features of infective endocarditis
Murmer (85%) + fever
Septic signs and symptoms of infective endocarditis
- fevers, rigors and night sweats
- malaise
- weight loss
- splenomegaly
- clubbing
Signs of subacute infective endocarditis
Usually due to immune-complex depositions and vasculitis
- Petechiae and splinter haemorrhages
- Janeway lesions: painless plantar/palmar lesions
- Osler’s nodes: painful infarcts in distal phalanges
- Roth spots: retinal haemorrhages with pale centre
- Glomerulonephritis
Risk Factors for infective endocarditis
Increased turbulent flow
* valve disease
* prosthetic valves
* structural disease: unrepaired PDA, VSD
* rheumatic heart disease
Increased pathogen entry and bacteraemia
* IV drug use
* haemodialysis
* dermatitis
Chronic disease
* Diabetes
* Kidney disease
Investigations in infective endocarditis
Blood cultures
* 3 sets from different sites before starting abx
* within 6 hours if subacute, within 1.5 hrs if acute
* 90% sensitive
Bloods
* FBC: normocytic anaemia
* ↑ neutrophils
* ↑ ESR/CRP
* Rheumatoid factor may be +ve (due to IE itself or RA)
Heart investigations
* Echo: transthoracic, then transoesophageal if -ve
* CXR: cardiomegaly
* ECG: ↑PR interval. Monitor to decide whether surgery required
Urinalysis: microhaematuria
Duke Criteria in Infective Endocarditis
Diagnosis requires any 1 of:
* 2 major
* 1 major plus 3 minor
* 5 minor
Major Criteria
* +ve blood culture x2 or persistent
* +ve echo: vegetation, abscess, new regurgitation, or prosthetic valve dehiscence
Minor criteria
* RF +ve
* fever
* vascular immune-complex signs
* +ve blood culture (x1)
* +ve echo for other abnormality
Acute Management of Infective Endocarditis
Abx as soon as blood cultures taken:
* 4-6 weeks, including at least 2 weeks IV initially
* Empiric therapy and for streptococci: benzylpenicillin (or amoxicillin) + gentamicin
* staph. aureus: flucloxacillin if native valve, add rifampicin and gentamicin if prosthetic valve
Surgery:
* Debridement, repair or replacement required in 20%
* Indications: refractory HF, persistant sepsis or emboli, or fungal IE
Bacterial causes of meningitis
- <3 months old = Group B strep
- 3 months - 45 yrs = neisseria meningitidis
- > 45yrs = strep. pneumoniae
- other causes = staph. aureus, e. coli, h. influenzae
- Listeria monocytogenes: may occur in pregnancy, neonates, the alcohol misusers
Viral causes of meningitis
- enteroviruses; coxsackie, echovirus
- herpes simplex, HSV2 more than HSV1
- Mumps
- Measles
Fungal causes of meningitis
- Cryptococcus neoformans
- it has an insidious onset
Non-infectious causes of meningitis
- cancer: carcinomatous meningtitis
- drugs: co-amoxiclav, NSAIDs, IVIg, azathioprine
- Inflammatory and autoimmune sarcoidosis, SLE, Behcet’s
Epidemiology of meningitis
- 40% of cases of bacterial meningitis are in children aged <15 years
- Commonest in first few months of life, affecting 1/2000 per year, then incidence drops to around 1/100,000 per year for the rest of life
Symptoms of meningitis
- Classic triad: fever, stiff neck, headache/altered mental status
- vomitting
- photophobia
- mottled skin
- confusion
- seizures
- rigors
- cold hands and feet
Signs of meningitis
- Kernig’s sign: with hip and knee flexed, pain limits passive extension of the knee
- Brudzinskis sign: neck flexion leads to involuntary hip and knee flexion
- Both are around 10% sensitive and 90% specific for meningitis
- Cerebral oedema = loss of consciousness, papilloedema, and focal CNS signs
Meningococcaemia
* petechiae and purpura: look carefully all over including backs of legs etc
* septic shock: hypotension, ↓ capillary refill
* DIC
Risk Factors for meningitis
- immunosuppression, including complement deficiencies and asplenia
- Skull fracture or anatomical defects
- crowding: university halls, military barracks, Hajj
Investigations for meningitis
Bloods
* ↑WBC, ↑CRP
* U&Es and LFTs
* Blood culture +/- N. meningitidis PCR
* Coag: DIC
Lumbar puncture:
* CT and opthalmoscopy 1st if ↑ICP suspected
* Bacterial CSF: ↑polymorphs, ↑proteins, ↓glucose, bacteria on culture, gram stain. Listeria can be mixed polymorphs and lymphocytes
* TB CSF: ↑lymphocytes, ↑protein, ↓glucose, ZN stain +ve
* Viral CSF: ↑lymphocytes, viral PCR +ve
Other investigations
* Throat swab for N. meningitidis
* CXR: pneumococcal pneumonia, TB
Acute Management of meningitis
- resuscitate, including oxygen and fluids
- broad spectrum IV abx stat, e.g. cefotaxime. Add amoxicillin if age>50 or <3 months. Benzylpenicillin IM if pre-hospital
- dexamethasone IV if >3months old: ↓neurological complications, but doesn’t affect mortality
Public health measures for meningitis
- notify public health about any case of meningitis or meningococcaemia
- isolate patient
- prophylactic abx: single dose of ciprofloxacin or 2 days of rifampicin. Give to all close contacts from the last 7 days, regardless of vaccination status
Complications of meningitis
- short term: ↑ICP, shock, DIC, subdural effusions, SIADH, seizures, venous sinus thrombus
- long term: cranial nerve palsies, deafness, limb amputation, memory or cognitive problems
Prognosis of meningitis
- 5% mortality rate in meningococcal
- 25% mortality rate in pneumococcal
- 35% mortality rate for listeria
What is encephalitis
Inflammation of the brain
Viral Causes of encephalitis
Most common
* Herpes simplex (HSV1>HSV2)
* VZV
* EBV
Others
* CMV
* HIV seroconversion
* measles
* mumps
* arboviruses (west Nile, Japanese, tick borne, St Louis)
* rabies
Other causes of encephalitis
- Autoimmune
- Idiopathic
- bacterial meningitis –> meningoencephalitis
- TB
- protozoa: malaria
- fungal: Aspergillus,Cryptococcus
Epidemiology of encephalitis
- annual incidence: 1/20,000
- Most common under 1 year old or over 65
Signs and Symptoms of Encephalitis
- Initially non-specific: fever, headache, nausea, vomiting, malaise
- Neuro symptoms: seizures, odd behaviour or confusion, ↓level of consciousness, focal signs
History for Encephalitis
include travel and bite exposure
Investigations for encephalitis
Bloods
* blood culture
* serum viral PCR
* If suspected: toxoplasma IgM, malaria film
Image with MRI or contrast-enhanced CT
* Temporal lobe inflammation: usually HSV or autoimmune
* meningeal irritation: meningoencephalitis
Special tests
* LP: ↑protein (most causes), ↑lymphocytes (viral, autoimmune), ↑PMNs (bacterial), ↓glucose (bacterial). Identify pathogen with viral PCR and gram stain
* EEG: optional
Management of Encephalitis
- Aciclovir IV stat to cover HSV. Continued for 14-21 days if HSV confirmed
- Consider ganciclovir for CMV if immunocompromised
- anticonvulsants for seizures
- autoimmune encephalitis: immunosuppressants (steroids, IVIg, plasma exchange) and treat for any underlying cancer
- If infectious notify public health authorities
Complications of encephalitis
- Short term: seizures, ↑ICP, SIADH, diabetes insipidus
- Long term: neurological complications, including motor and cognitive problems
Prognosis of encephalitis
- 10% mortality overall
- For HSV, treatment reduces mortality from >50% to 20%
Pathogens that cause gastroenteritis
- Viral: norovirus, rotavirus, astrovirus, adenovirus
- Bacteria: campylobacter jejuni, salmonella (usually S. enteriditis), shigella, E. coli, vibrio cholera, clostridium difficile
- protozoa: giardia, cryptosporodium, cyclospora, entamoeba
Transmission of gastroenteritis
- most are faecal-oral, and can be person to person, water-borne or foodborne
- some are zoonotic
- campylobacter, shigella and giardia can be sexually transmitted, especially in MSM
Signs and symptoms of gastroenteritis
- acute diarrhoea and/or vomitting
- anorexia
- malaise
- fever
- weight loss
Investigations in gastroenteritis
- most cases require minimal if any
- stool culture and microscopy if there is bloody stool, the patient is immunocompromised, there is recent travel to the developing world, or symptoms are prolonged (>7 days)
- Basic bloods if unwell: FBC (↑WBC), U&E (dehydration), CRP, LFT
Management of gastroenteritis
most cases do not require admission and can be managed at home with regular oral fluid intake
Inpatient management
* fluids (PO or IV)
* anti-emetics or anti-diarrhoeals if severe (do not give in dysentry)
* abx if systemically unwell or immunocompromised. Ciprofloxacin (campylobacter, salmonella, shigella) or tetracycline (V. cholera)
Infection control
* isolate patients with D+V
* any food poisoning or suspected food poisoning is a notifiable disease
Complications of gastroenteritis
- lactose intolerance
- Guillian-Barre syndrome
- Reactive arthritis
- Haemolytic uraemic syndrome after E. coli
Pathophysiology of C. diff infection
- gram +ve anaerobic bacillus
- transmitted by spores from people or the environment
- often follows abx course, especially clindamycin, cephalosporins or quinolones, which eliminate gut commensals (usually post 4-9 days, but can be up to 8 wks)
Presentation of C. diff infection
- Profuse watery diarrhoea. Bloody stool can occur but is rare
- abdominal pain and tenderness
- fever
Investigations in C. diff infection
- ↑WBC, sometimes very elevated. ≥15 = severe c. diff
- U&E. AKI = severe c. diff
- Stool PCR ± toxin immunoassay to confirm
Management in c. diff infection
- Stop any abx which may be causing it
- none-severe and sever: vancomycin PO = 1st line, fidaxomicin PO if vancomycin ineffective
- Life-threatening (shock, ileus, or megacolon): vancomycin PO/PR ± metronidazole IV. May need colectomy if there is toxic megacolon
- Consider faecal microbiota transplantation for recurrent disease
Complications of C. diff infection
- pseudomembranous colitis
- toxic megacolon
What is bacteriuria
bacteria in urine. may or may not be symptomatic
What is a UTI
significant bacteriruria (≥100,000 colony forming units/mL in MSU) + symptoms
What is a complicated UTI
UTI in the presence of certain risk factors, including renal or urinary tract abnormality, voiding difficulty, ↓ kidney function, indwelling catheter, immunosuppression, or virulent organism
Pathogens that cause UTIs
- E. coli (90%)
- Staph. saprophytics: occurs in sexually active women
- proteus mirabilis: suggests kidney stones
- enterococcus facealis: causes prostatis
- Klebsiella: usually in catheterised patients
- Staph. aureus: from haematogenous spread
- STIs: chlamydia, gonorrhoea
Epidemiology
- annual incidence: 1/10 women, 1/100 men
- Lifetime risk: 1/2 women, 1/20 men
- Risk increases with age
- Although less common in men, they account for 40% of UTI hospitalisations
Symptoms of UTIs
- cystitis (lower UTI): frequency, urgency, dysuria, nocturia, haematuria, suprapubic ache
- acute pyelonephritis (upper UTI): fever ± rigors, loin pain, systemically unwell (e.g. vomiting)
Signs of UTIs
- fever
- suprapubic or loin tenderness
- cloudy or smelly urine
- swollen, boggy, tender prostate (prostatitis)
- Discharge (STI urethritis)
Risk Factors for UTIs
- demographic: female, age
- pregnancy
- pathogen exposure: sexually active, catheter
- stagnant flow: obstruction (prostate, stones), retention, extended holding
- infection prone states: diabetes, immunosuppression
Other differential diagnoses alongside UTI signs/symptoms
- overactive bladder
- STIs
- non-infectious inflammation: atrophic vaginitis, interstitial cystitis
- vaginitis
- stones
- bladder or renal cancer
Investigations for UTIs
Urine dipstick:
* nitrites or leukocytes esterase +ve
* if +ve: start treatment and send MSU for M,C&S
* If -ve: send MSU anyway if strong clinical suspicion, male, child, pregnant or immunosuppressed
MSU MC+S
* Microscopy shows leukocytes ± bacteria
* If <100,000 CFU/mL but pyuria (>20 WBC/mm3) = sterile pyuria (prev. treated UTI, prostatitis, STI, TB, appendicitis, bladder tumour, stones, PKD)
* if many different organisms, suspect contaminated (not mid-stream) and repeat MSU
Further investigations if indicated
* pyelonephritis: FBC, U+E, CRP, blood cultures
* Blood glucose to rule out diabetes
* Imaging: kidney US (obstruction/hydronephrosis), post-void bladder US, CT KUB (stones)
General Approach to manage UTIs
- Abx if symptomatic
- paracetamol +/or NSAIDs for symptom relief
- remove catheter if present
Treatment of lower single UTI in women
- nitrofurantoin (if eGFR≥45) or trimethoprim PO for 3 days
- pregnancy: treat even if asymptomatic. Nitrofurantoin 1st line (unless at term), amoxicillin or cefalexin 2nd line, all PO for 7 days
- any other complicated UTI: trimethoprim or nitrofurantoin PO for 7 days
Preventing recurrent UTI in women
- behavioural and lifestyle: increase daily water intake, pre/post coital washing, avoid spermicides and diaphragm
- consider vaginal oestrogen if post-menopausal
- prophylactic abx if very disruptive: nitrofurantoin if eGFR≥45 or trimethoprim PO taken post-coitus if sex-related, otherwise daily
Urology referral and imaging indications for UTI
- failure of other measures
- has risk factors for urinary tract abnormality: obstructive symptoms, history of stones, urinary tract surgery, gynae cancer
- immunosuppressed
- recurrent UTI with haematuria: urgent referral for suspected cancer
Treatment of lower UTI in men
- nitrofurantoin (if eGFR≥45) or trimethoprim PO 7 days for cystitis
- ciprofloxacin PO for 2-4 wks if there if prostatis, IV if severely unwell
Treatment for upper UTI
- most upper UTIs are uncomplicated and can be managed with PO abx (cefalexin or ciprofloxacin for 7-10 days)
- if there is no response within 24hrs, signs of sepsis or in complicated UTI = hospitalisation and consider IV abx, e.g. 2nd-3rd generation cephalosporin or ciprofloxacin
Complications of UTIs
- infectious spread: pyelonephritis, perinephric or intrarenal abscess, prostatis, sepsis
- Kidney: AKI, hydronephrosis
- recurrence: 1 in 3 women, usually reinfection (new pathogen)
Prognosis of UTIs
symptoms resolve in 3-4 days with an effective abx, vs 5-7 days without treatment (or with a resistant organism)
What is cellulitis
Inflammation of dermis and subcutaneous tissue. Most commonly group A strep, then staph aureus
Signs and symptoms of cellulitis
Skin:
* inflammation: painful, red, hot, swollen
* poorly demarcated
* precipitating lesion: trauma, ulcer, bite, skin damage from chronic condition
* may have associated skin abscess
non-dermal features:
* lymphadenopathy
* systemic symptoms: fever
Common sites for cellulitis
- lower legs (NOTE: bilteral lower leg cellulitis is rare, consider venous eczema)
- canula site
Risk factors for cellulitis
- previous cellulitis
- chronic disease: diabetes, chronic kidney disease or liver disease, cancer
- immunodeficiency
- venous insufficiency
- age
- skin disease, e.g. tinea pedis
Investigations for cellulitis
Affected area:
* look for portal of entry and ask about trauma
* draw around edge of area to monitor progress
* swab for culture only needed for severe/resistant infections, or unusual exposures (penetrating injury, water-born, acqiured abroad)
Bloods if systemic symptoms:
* ↑WBC and ↑CRP
* Blood cultures
Investigate associated conditions
* foot Xray for osteomyelitis
* D-dimer, ultrasound and Well’s score if suspected DVT