Infectious Diseases Flashcards
Fever in a Returned Traveller
Differential Diagnoses
Specific History Questions
Clinical Features
1.) Differential Diagnoses
- dengue fever, malaria, typhoid (enteric) fever
2.) Specific History Questions
- travel within last 12 months, dates, duration of stay
- types of accom (rural vs urban), visiting family?
- insects? (malaria, rickettsia), animals? (bites/ticks)
- freshwater lakes/streams? (schistosomiasis)
- well/canal water? (leptospirosis)
- sexual hx, PMH
3.) Clinical Features
- febrile illness, diarrhoea +/- vomiting, jaundice, rash
- lymphadenopathy, hepatosplenomegaly
- resp sx: cough, SOB
Malaria
Organism
General Information
Clinical Features
Investigations
Management
1.) Organism - sporozoans, intracellular parasites
- Plasmodium falciparum/vivax/ovale
- definitive host (mosquitoes) is where sexual reproduction takes place, intermediate host (RBCs) is where asexual reproduction occurs
- merozoites invade RBCs causing them to eventually rupture releasing more merozoites
2.) General Information - blood protozoa/parasite
- incubation period: all >6 days, P. falciparum (up to 4 weeks), P. vivax/ovale (up to 1 year+)
- transmission: Anopheles mosquito bites (vector)
- location: sub-Saharan Africa (falciparum) and south Asia (ovale/vivax), central/south America
3.) Clinical Features - sudden onset rigors followed by:
- cyclical fevers, malaise, severe headaches, myalgia, abdo pain (vague), N+V, diarrhoea
- jaundice, hepatosplenomegaly
- signs: ↑HR, ↓BP, ↓BG, ↓Hb, ↓plts
- complications: AKI, DIC, neuro (confusion, convulsions), pulmonary oedema
4.) Investigations
- FBC (↓Hb, ↓plts, ↓WCC), ↑CRP, LFTs (↑bilirubin),
- U+Es (pre-renal AKI), ↓CBG, VBG/ABG (lactate)
- blood film (malarial parasites in RBCs), 3 negative blood films required before you can exclude malaria
- CXR (pulmonary oedema), CT head (if neuro sx)
5.) Management
- supportive: NSAIDs, paracetamol, fluids, rest
- severe falciparum: IV artesunate
- uncomplicated falciparum: PO Riamet (Artemether + lumefantrine) OR doxycycline + quinine (disrupts parasite replication and transcription)
- vivax/ovale: primaquine+chloroquine (screen G6PDH)
- prevention: clothing, chemoprophylaxis
Typhoid (Enteric) Fever
Organism
General Information
Clinical Features
Investigations
Management
1.) Organism - Salmonella typhi, S paratyphi A/B/C
- gram-negative bacilli, aerobic
- virulence factors: fimbriae (adhere to epithelium over payer’s patches), RES invasion, survives gastric acid
2.) General Information
- incubation period: 10-21 days
- transmission: faecal-oral from infected food/water
- location: SE Asia, south/central America, Africa
3.) Clinical Features
- vague abdominal pain, fever, malaise, dry cough
- constipation or diarrhoea, anorexia, hepatosplenomegaly
- rose spots (pink macules on chest or abdomen)
- pulse-temp dissociation (HR lower than expected)
- complication: intestinal haemorrhage/perforation
4.) Investigations
- FBC (↓Hb, ↓WCC, ↓lymphocytes), ↑CRP
- LFTs (↑ALT, AST, bilirubin)
- cultures: blood (2 required), stool, urine, bone marrow, duodenal
- CT abdo to exclude perforation
5.) Management
- IV ceftriaxone OD (broad) –> PO Ciprofloxacin BD OR PO azithromycin OD for 7-14 days
- vaccines (approx 70% efficacy)
Dengue Fever
Organism
General Information
Clinical Features
Management
1.) Organism - dengue virus
- female mosquitoes of Aedes aegypti
- 5 serotypes, infection with one type gives lifelong immunity to that type, infection w/ different type ↑risk of severe complications
2.) General Information
- incubation period: 7 days
- transmission: Aedes aegypti mosquito bites
3.) Clinical Features
- fever, myalgia and arthralgia
- pleuritic pain, headache (often retro-orbital)
- facial flushing (dengue), maculopapular rash
- complications: dengue haemorrhagic fever (form of DIC) which can progress to dengue shock syndrome
4.) Management - entirely symptomatic
- e.g. fluid resus, blood transfuion
- no antiviral available, vaccines available
Clostridium Difficile
Pseudomembranous Colitis
Clinical Features
Investigations
Management
Complications
1.) Pseudomembranous Colitis
- occurs after normal gut flora are suppressed by broad-spectrum antibiotics (PO/IV/IM)
- can affect any part of the colon
- opportunistic: elderly and immunosuppressed
- C diff can be found in up to 25% of asymptomatic hospitalised patients on antibiotics
- formation of spores makes C diff very difficult to destroy
2.) Clinical Features
- abdominal pain, profuse diarrhoea, fever
- raised WCC is characteristic but can be normal in mild disease
- severe disease: temp >38.3, WCC >15, raised CRP, AKI, albumin <25, endoscopic or radiologic evidence of severe colitis
3.) Investigations
- bloods: FBC, CRP, U+Es, clotting, blood cultures
- stool sample: +ve for C diff. toxin A/B and antigen
- AXR: thumbprinting and mucosal oedema, also to exclude toxic megacolon
- CXR: to exclude perforation (pneumoperitoneum)
- sigmoidoscopy: pseudomembrane formation
4.) Management
- treat the patient in a side room
- IV fluids, analgesia, stop/change current antibiotics
- mild: PO metronidazole (10-14 days) (IV if no enteral route)
- severe: PO vancomycin (10 days), (IV metro if no enteral route)
- avoid opiates and anti-diarrhoeal medications
5.) Complications
- toxic megacolon, perforation/peritonitis, sepsis
- AKI, hypoalbuminaemia, hypokalaemia
Tuberculosis
Risk Factors
Clinical Features
General Management
1.) Risk Factors - for screening for latent TB
- immigrants from high prevalence countries (South Asia, sub-Saharan Africa), healthcare workers
- HIV positive, patients starting on immunosuppression
- other risk factors: close contacts, IVDU, homeless
2.) Clinical Features - gradual onset (weeks or months)
- non-resolving cough, can be dry or productive
- unexplained fever, night sweats, weight loss
- lymphadenopathy, hepato/splenomegaly
- clubbing, cachexia, erythema nodosum
- signs of pleural effusion or pericardial rub
3.) General Management
- treated in a negative pressure side room
- can start treating for pneumonia if unsure
- considered non-infectious after 2 weeks of treatment
- contact tracing by TB nurses to screen for latent TB
- notifiable disease: notify public health England
- BCG vaccine given to high-risk patients (not given to HIV patients because it is a live attenuated vaccine)
Antibiotic Therapy for Tuberculosis
Baseline Assessments
Antibiotics + Side Effects
Additional Information
Latent TB
1.) Antibiotics + Side Effects
- Rifampicin (6mths): hepatitis, rashes, orange tears/urine, fever, many DDIs (inc warfarin and OCP)
- Isoniazid (6mths): w/ pyridoxine (vitB6) to prevent peripheral neuropathy, hepatitis, rashes, psychosis, colour blindness
- Pyrazinamide (2m): hepatitis, rashes, N/V, arthralgia
- Ethambutol (2mths): retrobulbar neuritis, visual loss
- RIFEATER = all 4, RIFINAH = rifampicin + isoniazid
- doses are weight dependent
2.) Monitoring
- before treatment: LFTs, visual acuity (ethambutol)
- during treatment: monitor LFTs, if deranged, stop and then gradually reintroduce when normalised
- can use directly observed therapy if low compliance
3.) Additional Information
- worsening symptoms upon starting because the bacteria dying causes an increase in inflammation
- steroids given at start of treatment to ↓inflammation if in sites additional swelling cannot be tolerated (meningeal, spinal, pericardial TB)
4.) Latent TB - treat >35s (↑risk of hepatotoxicity) only if other risk factors for TB (e.g. HIV or healthcare worker)
- Rifampicin + Isoniazid (3 months) OR Rifampicin monotherapy for 6 months
Investigations in Tuberculosis
Biopsy/Samples
Imaging
Screening for Latent TB
1.) Biopsy/Samples - culture can take up to 6 weeks
- pulmonary TB: sputum culture microscopy (Ziehl-Nielsen stain), bronchoscopy +/- EBUS if ‘smear negative’
- meningeal TB: lumbar puncture for culture and PCR
- lymph node TB: core biopsy of lymph node
- pericardial TB: ideally pericardiocentesis
- GI TB: colonoscopy and bowel biopsy
- histology: granuloma w/ central caseous necrosis w/ Langhans giant cell (known as tubercles)
2.) Imaging
- CXR: pulmonary shadowing, cavitating lesions (often lung apex), mediastinal lymphadenopathy, streaky fibrosis, flecks of calcification, pleural effusion
- CT: lymphadenopathy, can see lesions in viscera
- MRI: leptomeningeal enhancement in TB meningitis
3.) Others
- bloods: FBC, CRP, U+Es, LFTs, vit D
3.) Screening for Latent TB - in patients w/ risk factors
- QuantiFERON test: not affected by BCG vaccine, can get false positives in immunocompromised
- tuberculin skin test (Mantoux test)
- Chest XR
Extrapulmonary TB
TB Meningitis/CNS TB
Pericardial TB
Disseminated/Miliary TB
1.) TB Meningitis/CNS TB
- varied sx: personality change, headache, meningitic, comatose, more insidious onset than viral/bacterial
- exclude in patients w/ miliary TB (lumbar puncture)
- LP: high protein, low glucose, lymphocytosis
- MRI shows leptomeningeal enhancement
- steroids given, treatment is longer (12 months)
2.) Pericardial TB
- cause pericardial effusion –> cardiac tamponade
- pericardial rub or Kussmaul’s sign
- steroids given, treatment duration is 6 months
3.) Disseminated/Miliary TB
- CXR/CT: widespread, found in multiple sites inc CNS, bone marrow, pericardium
- CT/MRI head +/- LP to exclude CNS involvement
- do not delay treatment whilst waiting for biopsies
HIV (Human Immunodeficiency Virus)
Pathophysiology
Transmission and At-Risk Groups
Clinical Features
1.) Pathophysiology - single-stranded RNA retrovirus that infects and replicates with CD4 cells (Th cells)
- reverse transcriptase converts ssRNA into dsDNA
- seroconversion: primary infection where the body starts producing detectable levels of HIV antibodies
- ↓CD4 in response to initial, rapid replication of HIV, this is where the patient is extremely infectious
- over the next months-years, infection can become latent with ↓CD4 and ↑viral load, eventually, it becomes sx and develops into AIDS (avg 10 years)
2.) Transmission and At-Risk Groups
- UPSI (inc oral): MSM, high prevalence areas, UPSI with a partner who has lived/travelled in Africa
- needle-sharing: IV drug users
- vertical: during utero, childbirth or breastfeeding (can have a vaginal delivery if undetectable viral load)
- medical procedures: blood products, skin grafts, organ donation and artificial insemination
3.) Clinical Features
- seroconversion illness (2-6wks post-exposure): fever, malaise, muscle aches, lymphadenopathy, pharyngitis, maculopapular rash
- latent phase: often just asymptomatic
- symptomatic HIV: weight loss, fevers, diarrhoea,
frequent minor opportunistic infections (HZV, thrush)
- AIDS-defining conditions: TB, CMV infection, pneumocystis jiroveci pneumonia (PCP),
non-Hodgkin’s lymphoma, Kaposi’s sarcoma,
Management of HIV
Investigations
Highly Active Antiretroviral Therapy (HAART)
Monitoring
Additional Management
1.) Investigations
- ELISA tests: test for serum/salivary HIV antibodies and p24 antigen, reliable 4-6wks after exposure but can take up to 3 months to develop antibodies
- rapid home-testing kits can give results in 30 mins, but have ↓accuracy and need confirming w/ ELISA
- contact tracing to help identify those at risk
2.) Highly Active Antiretroviral Therapy (HAART)
- the aim is to have an undetectable viral load (<50) and normal CD4 count (500-1200), this has an excellent prognosis with a low risk of transmission
- classes: reverse transcriptase inhibitors, protease inhibitors, integrase inhibitors, entry inhibitors
- these are combined into 1 tablet to be taken daily: Atripla, Stribild, Eviplera, Triumeq
- drugs are taken life-long, non-adherence to HAART can lead to resistant mutations, making Tx difficult
3.) Baseline Investigations
- diagnostic HIV test, CD4 count, HIV viral load
- HIV resistance profile, HLA B*5701 status
- FBC, U+Es, LFTs, bone profile, lipid profile
- serology: syphilis, hep B/C/A, Schistosoma (in Africa)
- IgG levels: toxoplasma, measles, varicella, rubella
4.) Additional Management
- CD4 <200: prophylactic PO Co-trimoxazole OD against PCP
- CD4 <50 : PO Azithromycin once weekly to prevent TB (MAI)
- CD4 <50: regular ophthalmology review to assess for CMV retinitis
- monitoring of cardiovascular risk factors and blood lipids due to increased risk of cardiovascular disease
- yearly cervical smears for women (instead of every 3 years)
- vaccinations: influenza, pneumococcal, hepA+B, polio/diphtheria/tetanus, avoid live vaccines
Preventing Transmission of HIV
Post-Exposure Prophylaxis
Preventing Transmission During Birth
Breastfeeding
1.) Post-Exposure Prophylaxis
- taken if suspicious of exposure within the last 72hrs
- course lasts 1 month: Truvada (OD), Raltegravir (BD)
- arrange for HIV testing after 12 weeks (3 months)
- given to babies depending on mother’s viral load:
- <50: zidovudine for four weeks
- >50: zidovudine, lamivudine, nevirapine for 4wks
2.) Preventing Transmission During Birth
- viral load <50: normal vaginal delivery
- viral load >50: consider C-section esp if >400
- unknown viral load or >10,000: IV zidovudine should be given during the caesarean
3.) Breastfeeding
- not recommended for mothers with HIV even with an undetectable viral load
Meningitis
What is it?
Causes
Clinical Features
Complications
1.) What is it? - inflammation of the leptomeninges and the CSF of the subarachnoid space
2.) Causes
- bacteria: N. meningitidis (young), S. pneumoniae (old), Listeria monocytogenes (immunosuppressed)
- viral: HSV, CMV, HIV, measles, mumps, enteroviruses
- others: TB, fungal
3.) Clinical Features
- fever, neck stiffness, photophobia, vomiting
- headache, confusion,
- septicaemia: non-blanching purpuric rash, ↓BP (late)
- meningoencephalitis: seizures, focal neuro deficits
4.) Complications
- sensorineural hearing loss, epilepsy, paralysis
- sepsis, intracerebral abscess
- brian herniation, hydrocephalus
Management of Meningitis
Investigations
CSF Analysis
Management
Management of Close Contacts
1.) Investigations
- lumbar puncture: must exclude ↑ICP, L3/L4, between arachnoid mater and pia mater
- FBC: ↑WCC, ↓plts, ↑CRP, coagulation screen, VBG, blood glucose, blood cultures,
2.) CSF Analysis
- bacterial: cloudy, low glucose (<50% of CBG), high protein (>50mg/dL), majority neutrophils
- viral: clear/cloudy, normal glucose (>50% of CBG), normal/raised protein, majority lymphocytes
- TB/fungal: slightly cloudy, low glucose, high protein, majority lymphocytes
3.) Management
- GP: call an ambulance, give high flow oxygen, give IV (IM if no IV access) benzylpenicillin,
- IV ceftriaxone (or cefotaxime)
- IV dexamethasone to ↓risk of neuro complications unless septic or immunocompromised or post-op
- IV fluids, analgesia, ?sepsis 6
4.) Management of Close Contacts
- notify public health England
- prophylactic Abx (PO cipro or rifampicin) for close contacts (<7days) for meningococcal meningitis
- meningococcal vaccine for close contacts
