Infectious diseases Flashcards
1
Q
First thought cellulitis.
A
- Infection of dermis and subcutaneous tissue
- caused by: S. aureus, ß-haemolytic streptococci
- Flucloxacillin
2
Q
What is the aetiology of cellulitis?
A
- common causative agents: S. aureus, β-hemolytic streptococci
- immunocompromised patients or water exposure: may also include GN rods and fungi
- risk factors:
- trauma with direct inoculation, recent surgery
- peripheral vascular disease, lymphedema diabetes, cracked skin in feet/toes (tinea pedis)
3
Q
What are the clinical features of cellulitis?
A
- pain, edema, erythema with indistinct borders ± regional lymphadenopathy, systemic symptoms (fevers, chills, malaise)
- can lead to ascending lymphangitis (visible red streaking in skin along lymphatics proximal to area of cellulitis)
4
Q
What Ix are ordered for a pt with cellulitis?
A
- FBC and differential, blood C&S if febrile
- skin swab ONLY if open wound with pus
5
Q
What is the Rx for cellulitis?
A
- Abx
- Mild/early: di/flucloxacillin 500 mg PO, 6h for 5-10 days OR cephalexin for penicillin sensitivity
- Severe: flucloxacillin 2g IV, 6h Or cephazolin for penicillin sensitivity
6
Q
Describe the aetiology and risk factors of a septic joint?
A
- most commonly caused by Staphylococcus aureus in adults
- consider coagulase-negative Staphylococcus in patients with prior joint replacement
- consider Neisseria gonorrhoeae in sexually active adults and newborns
- most common route of infection is hematogenous
- risk factors: age >80 yr, DM, RA, prosthetic joint, recent joint surgery, skin infection/ulcer, IV drug use, alcoholism, previous intra-articular corticosteroid injection
7
Q
What is the clinical presentation of a septic joint?
A
- inability/refusal to bear weight
- localized joint pain
- erythema
- warmth
- swelling
- pain on active and passive ROM
- ± fever
8
Q
What investigations should be ordered for a suspected septic joint?
A
- Bloods: FBC, UEC, LFT, glucose, urate, CRP/ESR, blood cultures
- Urine: ward test → MCS if positive.
- x-ray (to rule out fracture, tumor, metabolic bone disease)
- Joint asperate: MCS, crystals
- WBC >80,000 with >90% neutrophils, protein level >4.4 mg/dL, joint glucose level << blood glucose level, no crystals, positive Gram stain results
- Listen for heart murmur (to reduce suspicion of infective endocarditis)
9
Q
What is the Rx for septic arthritis?
A
- IV antibiotics, empiric therapy (based on age and risk factors), adjust following joint aspirate C&S results:
- Flucloxacillin 1g/6h IV - ?empirical
- Vancomycin 1g/12h IV if MRSA
- Cefotaxine 1g/8h IV if gonococcal or Gram-ve
- for small joints: needle aspiration, serial if necessary until sterile
- for major joints such as knee, hip, or shoulder: urgent decompression and surgical drainage - Ortho referral for arthrocentesis, lavage and/or debridement
- Give adequate analgesia
10
Q
What is the classification of a prosthetic joint infection?
A
- Early (<3 months after surgery) - acquired during implantation
- Delayed (3 - 12 months after surgery) - acquired during implantation
- Late (>12 months) - primarily due to haematogenous (sudden onset in a previously well-functioning joint)
11
Q
What is the aetiology of a prosthetic joint infection?
A
- Early post-operative: virulent organisms - Staphylococcus aureus but also beta-haemolytic streptococci and aerobic Gram-negative organisms.
- Chronic infections: are likely to be caused by less virulent organisms, including coagulase-negative staphylococci, Enterococcus species and Propionibacterium species
- Late acute haematogenous infections: Virluent organisms - Staphylococcus aureus but also beta-haemolytic streptococci and aerobic Gram-negative organisms.
12
Q
What is the Rx for a prosthetic joint infection?
A
- Multidisciplinary team approach
- Abx to culture and sensitivities
- Empiral Rx use - Vancomycin IV
- Ortho - tissue biopsy and specimen of synovial fluid intraopertatively
- removal of prosthesis in some cases
- exchange arthroplasty
13
Q
Define S aureus bacteremia.
A
- S. aureus bacteremia is defined as positive blood cultures for S. aureus; frequently, this occurs in association with correlating symptoms such as fever or hypotension.
- S. aureus is a leading cause of community-acquired and hospital-acquired bacteremia.
- Bacteremia may develop as a complication of a primary S. aureus infection such as skin and soft tissue infection, bone and joint infection, or pneumonia.
- Vascular catheters are a common source of bacteremia.
- Bacteremia may also lead to subsequent S. aureus infection at a previously sterile site, such as endocarditis or prosthetic device infection.
14
Q
Whar is your clinical appraoch towards a patient with potential S aureus bacteremia?
Hx and exam
A
- Hx
- Portals of entry: skin or soft tissue, indwelling prosthetic devices
- Symptoms: reflecting metastatic infectyion
- bone or joint pain
- protracted fever or sweats
- abdo pain
- costovertebral angle tenderness and headache
- Exam:
- Cardiac: new regurgitant murmurs or heart failure, stigmata of endocarditis
- Neuro: focal neuro impairment and baseline neuro incase deficits develop
15
Q
What is the Rx for S aureus bacteremia?
A
- ID consult
- Echo - rule out endocarditis
- Removal of source
- Abx
- Empirical - Vancomycin IV
- MSSA - flucloxacillin IV q6h or cefazolin 2g IV q8h
- MRSA - Vancomycin IV
- Follow-up cultures to document clearance of bacteraemia
16
Q
Define what a urinary tract infection is?
A
- symptoms suggestive of UTI + evidence of pyuria and bacteriuria on U/A or urine C&S
- if asymptomatic + 100,000 CFU/mL = asymptomatic bacteriuria; only requires treatment in certain patients (e.g. pregnancy)
17
Q
How are UTIs classified?
A
- uncomplicated: lower UTI in a setting of functionally and structurally normal urinary tract
- complicated: structural and/or functional abnormality, male patients, immunocompromised, diabetic, iatrogenic complication, pregnancy, pyelonephritis, catheter-associated
- recurrent/chronic cystisis: ≥3 UTIs/yr
18
Q
What are the risk factors for getting a UTI?
A
- stasis and obstruction
- residual urine due to impaired urine flow e.g. PUVs, reflux, medication, BPH, urethral stricture, cystocele, neurogenic bladder
- foreign body
- introduce pathogen or act as nidus of infection e.g. catheter, instrumentation
- decreased resistance to organisms
- DM, malignancy, immunosuppression, spermicide use, estrogen depletion, antimicrobial use
- other factors
- trauma, anatomic abnormalities, female, sexual activity, fecal incontinence
19
Q
What are the clinical features of UTI?
A
- storage symptoms: frequency, urgency, dysuria
- voiding symptoms: hesitancy, post-void dribbling
- other: suprapubic pain, hematuria, foul-smelling urine
- pyelonephritis – if present: typically presents with more severe symptoms (e.g. fever/chills, CVA tenderness, flank pain)
20
Q
What are the organisms that are usually involved in UTI?
A
- typical organisms: KEEPS
- Klebsiella sp.
- E. coli (90%), other Gram-negatives
- Enterococci
- Proteus mirabilis, Pseudomonas
- S. saprophyticus
- atypical organisms
- tuberculosis (TB)
- Chlamydia trachomatis
- Mycoplasma (Ureaplasma urealyticum)
- fungi (Candida)
21
Q
What are the indications for investigation of UTI?
A
- pyelonephritis
- persistence of pyuria/symptoms following adequate antibiotic therapy
- severe infection with an increase in Cr
- recurrent/persistent infections
- atypical pathogens (urea splitting organisms)
- hx of structural abnormalities/decreased flow
22
Q
What investigations should be order in UTI?
A
- U/A, urine C&S
- UA: leukocytes ± nitrites ± hematuria
- C&S: midstream, catheterized, or suprapubic aspirate
- if hematuria present, retest post-treatment, if persistent need hematuria workup
- U/S, CT scan if indicated
23
Q
What is the treatment for UTI?
A
- Non-pregant women/men: trimethoprim 300mg PO for 3 days
- Pregnant women: cephalexin 500mg PO 12h for 5 days
24
Q
What microbes usually cause surgical site infections?
A
- S. aureus
- E. coli
- Enterococcus
- Streptococcus spp.
- Clostridium spp.
25
Q
What are the risk factors for a surgical site infection?
A
- patient characteristics
- age, DM, steroids, immunosuppression, obesity, burn, malnutrition, patient with other infections, traumatic wound, radiation, chemotherapy
- other factors
- prolonged pre-operative hospitalisation, reduced blood flow, break in sterile technique, multiple antibiotics, haematoma, seroma, foreign bodies (drains, sutures, grafts), skin preparation, hypoxaemia, hypothermia
26
Q
What is the clinical presentation of a surgical site infection?
A
- typically fever POD #5-8 (Streptococcus and Clostridium can present in 24h)
- pain, blanchable wound erythema, induration, purulent discharge, warmth
- complications: fistula, sinus tracts, sepsis, abscess, suppressed wound healing, superinfection, spreading infection to myonecrosis or fascial necrosis (necrotizing fasciitis), wound dehiscence, evisceration, hernia
27
Q
What can be done as prophylaxis for surgical site infections?
A
- used to reduce the chance of surgical site infections pre-operative antibiotics for most surgeries (cefazolin ± metronidazole or if β-lactam allergy, clindamycin ± gentamycin)
- within 1 h pre-incision; can re-dose at 1-2 half-lives (~q4-8h) in the OR
- not required for low risk elective cholecystectomy, hemorrhoidectomy, fistulotomy, sphincterotomy for fissure
- generally no need to continue prophylactic antibiotics post-operatively
- reserve post-operative antibiotics for treatment of suspected or documented intra-abdominal infection
- normothermia (maintain patient temperature 36-38ºC during OR)
- hyperoxygenation (consider FiO2 of 80% in OR)
- chlorhexidine-alcohol wash of surgical site
- hair removal should not be performed unless necessary; if so, clipping superior to shaving
- protect skin edges (moistened lap pads); consider delayed primary closure of incision for contaminated wounds
28
Q
What is the Rx for surgical site infections?
A
- examination of the wound: inspect, compress adjacent areas, swab drainage for C&S and Gram stain
- re-open affected part of incision, drain, pack, heal by secondary intention in most cases
- for deeper infections, debride necrotic and non-viable tissue
- antibiotics
- demarcation of erythema only if cellulitis or immunodeficiency
29
Q
Describe the aetiology of diabetic foot infections.
A
- neuropathy, peripheral vascular disease, and hyperglycemia contribute to foot ulcers that heal poorly and are predisposed to infection
- organisms in mild infection: S. aureus, Streptococcus spp.
- organisms in moderate/severe infection: polymicrobial with aerobes (S. aureus, Streptococcus, Enterococcus, GNB) and anaerobes (Peptostreptococcus, Bacteroides, Clostridium)
30
Q
What are the clinical features of diabetic foot infections?
A
- NOT all ulcers are infected
- consider infection if: probe to bone, ulcer present >30 d, recurrent ulcers, trauma, PVD, prior amputation, loss of protective sensation, renal disease, history of walking barefoot
- diagnosis of infected ulcer: ≥2 of the cardinal signs of inflammation (redness, warmth, swelling, pain) or the presence of pus
- ± crepitus, osteomyelitis, systemic toxicity
- visible bone or probe to bone → osteomyelitis
- infection severity:
- mild = superficial (no bone/joint involvement)
- moderate = deep (beneath superficial fascia, involving bone/joint) or erythema >2 cm
- severe = infection in a patient with systemic toxicity (fevers, tachypnea, leukocytosis, tachycardia, hypotension)
31
Q
What investigations need to be order with a patient with a diabetic foot infection?
A
- curettage specimen from ulcer base, aspirate from an abscess or bone biopsy (results from superficial swabs do not represent organisms responsible for deeper infection)
- blood C&S if febrile
- assess for oseteomyelitis by x-ray (although not sensitive in early stages) or MRI if high clinical suspicion
- if initial x-ray normal, repeat 2-4 wk after initiating treatment to increase test sensitivity
32
Q
What is the Rx for diabetic foot infection?
A
- evaluate for early surgical debridement ± revascularization or amputation
- eliminate/reduce pressure and provide regular local wound care
- mild to moderate: Amoxycillin + clavulanate 875 + 125 mg PO 12h
- severe: piperacillin/tazobactam 4 + 0.5 g IV q8h
- encourage glycemic control
33
Q
What is the DDx of fever in the returned traveller
A
- commonly identified causes of fever in returning traveler
- parasitic: malaria (20-30%)
- viral: non-specific mononucleosis-like syndrome (4-25%), dengue (5%), viral hepatitis (3%)
- bacterial: typhoid from Salmonella (2-7%), rickettsioses (3%)
- diverse group of causative pathogens: traveler’s diarrhea (10-20%), RTI (10-15%), UTI/STD (2-3%)
- febrile illness in travelers can be caused by routine infections that are common in non-travelers (e.g. URTI, UTI)
- less commonly, fever can be due to non-infectious causes: e.g. DVT, PE
34
Q
What information do you want to collect from a patient who is a returned traveller with a fever?
A
- pre-travel preparation
- travel itinerary: when, where, why, what, who, how?
- dates of travel (determine incubation period)
- season of travel: wet or dry
- destination: country, region (urban or rural), environment (jungle, desert, etc.)
- purpose of trip
- persons visiting friends and family more likely to be exposed to local population and pathogens
- style of travel: lodgings, camping, adventure traveling
- local population: sick contacts
- transportation: use of animals
- exposure history
- street foods, untreated water: increased risk of traveler’s diarrhea, enteric fever
- uncooked meat/unpasteurized dairy: increased risk of parasitic infection
- body fluids (sexual contacts, tattoos, piercings, IVDU, other injections)
- increased risk of HBV, HCV, HIV, GC, C. trachomatis, syphilis
- animal/insect bites: increased risk of malaria, dengue, rickettsioses, rabies
- fever pattern
- incubation period: use the earliest and latest possible dates of exposure to narrow the differential diagnosis and exclude serious infections
- <21 d: consider malaria, typhoid fever, dengue fever, rickettsioses; exclude HBV, TB
- >21 d: consider malaria, TB; exclude dengue fever, travelers’ diarrhea, rickettsioses
- body systems affected: GI, respiratory, CNS, skin
35
Q
What investigations would you order in fever in a returned traveller?
A
- all travelers with fever should undergo the following tests
- blood work: FBC, LFT, UECs, thick and thin blood smears x3 (for malaria), blood C&S
- urine: urinalysis, urine C&S
- special tests based on symptoms, exposure history, and geography
- stool: C&S, O&P
- CXR
- dengue serology for IgM
36
Q
Describe the lifecycle of malaria (Plasmodium spp.).
A
- Sporozoites enter blood via mosquito bite, infect liver
- Hepatic infiltration
- Infect red blood cells
- Trophozoite divides asexually many times to produce schizont (contains merozoites)
- Red blood cell lyses and merozoites attack other red blood cells (chills and fever)
- Male and female gametocytes (from merozoites) ingested by mosquito
during bite - Male and female gametocytes (from merozoites) fuse in mosquito gut; produce ookinete
- Ookinete matures into an oocyst which contains individual sporozoites; migrates to mosquito salivary glands
37
Q
What are the clinical features of malaria?
A
- flu-like prodrome
- paroxysms of high spiking fever and shaking chills (due to synchronous systemic lysis of RBCs) (lasts several hours)
- P. vivax and P. ovale: chills and fever q48h but can be variable
- P. malariae: chills and fever q72h but can be variable
- P. falciparum: less predictable fever interval, can be highly variable (>90% ill within 30 d)
- abdominal pain, diarrhea, myalgia, H/A, and cough
- hepatosplenomegaly and thrombocytopenia without leukocytosis
38
Q
What are the complications of malaria?
A
- P. falciparum: CNS involvement (cerebral malaria = seizures and coma), severe anemia, acute renal failure, ARDS, primarily responsible for fatal disease
- P. knowlesi, and rarely P. vivax can be fatal
39
Q
What investigations are order for a pt with malaria?
A
- microscopy: blood smear q12-24h (x3) to rule out infection
- thick smear (Giemsa stain) for presence of organisms
- thin smear (Giemsa stain) for species identification and quantification of parasites
- rapid antigen detection tests
40
Q
What is the Rx for malaria?
A
- P. vivax, P. ovale: chloroquine (and primaquine to eradicate liver forms)
- P. vivax, chloroquine resistant: primaquine with quinine and doxycycline or tetracycline or mefloquine
- P. malariae, P. knowlesi: chloroquine
- P. falciparum: most areas of the world show chloroquine resistance – check local resistance patterns
- artemisinin combination therapy (e.g. artesunate + doxycycline or clindamycin or atovaquone/proguanil)
- atovaquone/proguanil combination (Malarone®)
- quinine plus doxycycline, tetracycline, or clindamycin
- mefloquine and artemisinin resistance increasing in southeast Asia (check local resistance)
- prevention with antimalarial prophylaxis, covering exposed skin, bed nets, insect repellant
41
Q
Describe the epidemiology and risk factors of discitis?
A
- Most cases occur in >50
- M>F = 2:1
- Risk factors:
- IVD use
- endocarditis
- degenerative spine disease
- prior spinal surgery
- corticosteroid therepy/immunocompromised state
42
Q
What are the organisms that responsible for discitis?
A
- Staph aureus (>50%)
- Enteric gram -ve bacilli - urinary tract instrumentation
- Pseudomonas aeruginosa and Candida spp. - associated with IVD
- Group B and G haemolytic streptococci - esp. in DM
- TB
43
Q
What are the clinical features of discitis?
A
- Back or neck pain - localised to the infected disc space, exacerbated by physical activity or percussion to the affected area.
- Radiating pain to the abdo, leg, scrotum, groin or perineum
- Spinal pain that begins insidiously and progressively worsens over weeks>months and worse at night
44
Q
What Ix should be order for a patient with discitis?
A
- Bloods: FBC, UECs, LFT, CRP/ESR, blood cultures,
- Urine: MCS
- Echo: endocarditis
- Imaging: CT guided needle bipsy (MCS), MRI
45
Q
What is the treatment for discitis?
A
- Abx: pathogen specific - for a min of 6 weeks
- Staph aureus: cefazolin 2g IV q8h
- Strep spp: ceftriaxone 1-2g IV q24h
- Empirial: vancomycin 15-20 mg/kg Q8-12h PLUS a cephalosporin
- Surgery: used only in patietns with neurological deficits
46
Q
Define meningitis.
A
Inflammation of the meninges
47
Q
What are the common organisms in meningitis?
A
49
Q
What are the risk factors for meningitis?
A
- lack of immunisation against S. pneumoniae, H. influenzae type b in children
- haematogenous spread after invasion from a mucosal surface (nasopharynx)
- parameningeal focus (otitis media, infection, sinusitis)
- penetrating head trauma
- anatomical meningeal defects – CSF leaks
- previous neurosurgical procedures, shunts
- immunocompromise (corticosteroids, HIV, asplenia, hypogammaglobulinemia, complement deficiency)
- contact with colonised or infected persons
50
Q
What are the clinical features of meningitis?
A
- neonates and children: fever, vomiting, lethargy, irritability, poor feeding
- older children and adults: fever, H/A, neck stiffness, confusion, N/V, lethargy, photophobia, altered level of consciousness, seizures, focal neurological signs, papilledema
- petechial rash in meningococcal meningitis, seen more frequently on trunk or lower extremities
51
Q
What Ix should be done for a pt with meningitis?
A
- blood work:
- FBC and differential, UEC (for SIADH), blood C&S
- CSF: opening pressure, cell count + differential, glucose, protein, Gram stain, bacterial C&S
- Acid fast bacilli, fungal C&S, cryptococcal antigen in immunocompromised patients, subacute illness, suggestive travel history or TB exposure
- PCR for HSV, VZV, enteroviruses, WNV if viral cause suspected
- imaging/neurologic studies:
- CT, MRI, EEG if focal neurological signs present
52
Q
Describe the typical CSF profiles for bacterial and viral meningitis?
A
62
Q
How is endocarditis diagnosed?
A
- Modified Duke Criteria
- definitive diagnosis if: 2 major, OR 1 major + 3 minor, OR 5 minor
- possible diagnosis if: 1 major + 1 minor, OR 3 minor
80
Q
Describe the aetiology and clinical presentation of both viral and bacterial causes of gastroenteritis?
What are the risk factors and management of both?
A
81
Q
What organisms are responsible for septic athrittis and osetomyelitis is children?
A
97
Q
Describe the invasion sites by HIV and the medium that is used to do so?
A
99
Q
Describe the illnesses that accompany the decreasing CD4 counts?
A
103
Q
What are the target sites for anti-retroviral drugs?
A
108
Q
What are the main types of hepatitis that can be acquired during travel in South-east asia or south asia and how can they be prevented?
A
111
Q
Illustrate bacterial wall structures in gram +ve and -ve bacteria.
A
