Course:PostgradFamilyPractice/ExamPrep/99 Priority Topics/Infections

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Infections - Key Features

1. In patients with a suspected infection,
a) Determine the correct tools (e.g., swabs, culture/transport medium), techniques, and protocols for cultures,
b) Culture when appropriate (e.g., throat swabs/sore throat guidelines).

1) Throat

a. Main objective in diagnosis is to rule out Group A Strep (GAS)
b. Clinical Decision Criteria (Centor Criteria):
i. Tonsillar Exudates
ii. Tender anterior cervical adenopathy
iii. Fever by history
iv. Absence of cough
Absence of 3/4 above criteria has negative predictive value of 80%
c. Throat culture specimen obtained by vigorous scrubbing of both tonsils and posterior pharynx. Over 90% sensitive and specific with proper technique.
d. Advise lab if N. gonorrhea is suspected (different plating method)
e. Rapid test lacks sensitivity but if + is diagnostic, provides a “same visit result”. ELISA technique used.
f. Consider serology for EBV mononucleosis with persisting symptoms and systemic involvement

2) Urine

a. No need to culture in symptomatic young women if uncomplicated UTI suspected w/ obvious sx of dysuria and frequency and pyuria on urinalysis.
b. Culture in young women if complicated infection, atypical sx, failed therapy, recurrence < 1mo post treatment.
c. A dipstick positive test (nitrites and/or leuks with blood) is a reliable indicator of significant bacteriuria but a negative test does not r/o bacteriuria. If sxs indicate, send for culture.
d. Nitrite positive indicates presence of Enterobacteriaceae (e.g. gram negative rods such as E.Coli or Klebsiella)
e. Keep urine sample in fridge if not sending to lab immediately.
f. Culture in ALL children, pregnant women, elderly and men. In men, consider ddx of prostatitis.

3) LP

a. Suspected CNS infection, subarachnoid hemorrhage, other weird things (NPH, tuberculosis, CNS vasculitis etc)
b. No absolute contraindications but relative include: overlying infection, suspected epidural abscess, thrombocytopenia, raised ICP - must do head CT before proceeding!

4) Skin

a. Cultures now should be routine for abscess drainage due to prevalence of MRSA, only swab pus from abscess, not wound.
b. Patients with abscess >5cm, multiple lesions, extensive surrounding cellulitis, immunosuppresion, systemic signs of infection or lack of response to I&D suggested to use antibiotics.

5) Sputum

a. No role in acute bronchitis in otherwise healthy individuals
b. Also no role in initial diagnosis of acute exacerbations of COPD
c. While a positive blood or pleural fluid culture definitively identifies the pathogen, an organism growing from a respiratory specimen is not definitive proof that it is the etiologic agent. Many bacterial species are normal flora or colonizers of the respiratory tract, and although present in respiratory secretions, they may not be responsible for the clinical illness in an individual patient with pneumonia due to another cause.
d. May play important role in aiding diagnosis of inpatient illness because bronchoscopy samples more reliable at isolating organisms.

6) Eye

a. Cultures are not necessary for the initial diagnosis and therapy of conjunctivitis, except in neonates
b. The exception is patients with symptoms of hyperacute conjunctivitis at risk for Neisseria gonorrhoeae.

7) Stool

a. Indications for stool culture include:
- diarrhea after possible pathogen exposure (e.g. recent travel)
- prolonged diarrhea (>5 days)
- diarrhea containing blood or mucous
- abdominal pain, cramping, nausea, vomiting, fever
- diarrhea with recent antibiotic therapy (C. difficile toxin test)

Enteric Bacterial Pathogens (send for stool C&S)

• Campylobacter jejuni
• Salmonella spp.
• Verotoxin producing E. coli (e.g., E. coli O157:H7)
• Shigella spp.
• Aeromonas spp. (toxin producing strains)
• Clostridium difficile
• Yersinia enterocolitica
• Pleisiomonas shigelloides

Enteric Protozoan Pathogens (send for stool O&P)

• Giardia lamblia (intestinalis)
• Cryptosporidium spp.
• Entamoeba histolytica
• Dientamoeba fragilis
• Microsporidium spp.
• Blastocystis hominis
• Cyclospora spp.
• Isospora belli

Enteric Viral Pathogens (usually reserved for pediatrics patients)

• Adenovirus 40/41
• Rotavirus
• Caliciviruses
• Astroviruses
• Norwalk virus

Vaginal swabs covered in Vaginitis Key Feature

2. When considering treatment of an infection with an antibiotic, do so
a) Judiciously (e.g., delayed treatment in otitis media, with comorbid illness in acute bronchitis),
b) Rationally (e.g., cost, guidelines, comorbidity, local resistance patterns).

For one of those handy charts for antibiotic spectra, here’s a massive one:

List of Reportable Diseases (Consistent with National Guidelines but Toronto’s is up to date for 2011)

Otitis Media
Further otitis media information in Earache Key Feature
From CPS Guideline 2009
-Watchful waiting appropriate for children older than 6 months of age without severe symptoms (appear toxic, severe otalgia and/or high fever (greater than 39C orally))
-Parents must be capable of recognizing signs of worsening illness and be willing and able to readily access medical care.

First-line therapy for child with no beta-lactam allergery = amoxicillin 75-90 mg/kg/day
For allergic, consider macrolide (clarithromycin, azithromycin)
5 days as effective as 10 days in children older than two years of age with uncomplicated AOM.

Acute Bronchitis
- Self-limiting inflammation of the bronchi due to upper airway infection - present with cough and sputum production for 1-3 weeks.
- One of the most common conditions associated with antibiotic misuse
- Most commonly caused by virus (influenza A and B, parainfluenza, coronavirus, rhinovirus, RS, metapneumonvirus) but still 60-90% of patients presenting with cough + sputum are given anbx!
- Cough disappears by day 14 in 75% of patients with acute viral bronchitis.
- Suspect Pertussis (even adults) with cough lasting longer than two weeks (partial immunity from prior immunizations) and send NPS swab.
- Sputum purulence does not signify bacterial infection
- If febrile, get CXR to r/o pneumonia
- DDx includes:

a. Chronic Bronchitis - cough + sputum for 3 months, 2 years in a row
b. Pneumonia
c. Postnasal drip
e. Asthma

Treat with antibiotics if:

1. At high risk of serious complications because of preexisting comorbidity (heart, lung, renal, liver, neuromuscular disease, or immunosuppression)
2. Patients over 65 years of age with acute cough and two or more of the following, or patients over 80 years of age with one or more of the following:
- Admission to hospital in the previous year
- Type 1 or type 2 diabetes
- History of congestive heart failure
- Current use of oral glucocorticoids

Common Antibiotics in Primary Care and their Estimated Cost to Patient for a 10 day Rx
(Rx Files 8th edition - 2010)

From least to most expensive:

Pen- V - $10
Metronidazole (Flagyl) - $11
Cotrimoxazole (Septra) DS - $10-12 for both peds and adult suspensions and tabs
Amoxicillin - $15 for peds suspensions, $17-27 for adult capsules
Azithromycin (Zithromax) - $21 for peds suspensions, $28 for adult tabs
Nitrofurantoin (Macrobid) - $23
Cephalexin (Keflex) - $25 for both peds and adult suspensions and tabs
Cefixime (Suprax) - $26 for peds suspensions, $49 for adult tabs
Minocycline (Minocin) - $31
Ciprofloxacin - $43
Clarithromycin (Biaxin) - $37-67 for adult tabs
Clindamycin (Dalacin) - $50
Moxifloxacin (Avelox) - $74

3. Treat infections empirically when appropriate (e.g., in life threatening sepsis without culture report or confirmed diagnosis, candida vaginitis post-antibiotic use).

Rationale for antibiotic treatment with Group A strep pharyngitis:

1. To prevent post streptococcal sequelae — anbx treatment can reduce incidence of acute rheumatic fever by 75%. No firm evidence to suggest that antibiotic therapy reduces incidence of poststreptococcal glomerulonephritis.
2. To prevent suppurative complications —Peritonsillar abscess, sinusitis, and retropharyngeal abscess. Peritonsillar abscess typically occurs in adolescents and young adults. Retropharyngeal abscess occurs most commonly in the first few years of life and sinusitis is a very rare complication of GAS pharyngitis.
3. To reduce symptoms — There is a modest (approximately one day) reduction in symptoms with early antibiotic treatment. A meta-analysis found that throat soreness and fever was reduced by about one-half at day three for patients treated with antibiotics, compared to those given placebo. For patients with GAS and severe symptoms (≥3 Centor criteria), symptoms resolved 2.5 days earlier with antibiotic therapy in one randomized trial.
4. To prevent transmission — While this is important in pediatrics, due to extensive exposures, it is considered far less important in adults.

Sepsis briefly:
SIRS Criteria:

- Temp less than 36°C or greater than 38°C
- HR greater than 90 bpm
- RR greater than 20 or PaCO2 less than 32mmHg
- WBC less than 4 or greater than 12, or presence of 10% bands

1. Sepsis = SIRS + probable source
2. Severe Sepsis = above plus evidence of end organ dysfunction (renal failure, hypotension, altered MS, ARDS, mottling etc
3. Septic Shock = above + MAP < 60 without pressers

Identify source: CXR, Urine, Blood Cultures x 2, sputum (usually if intubated); if sx indicate can order: throat swab, LP, wound/fluid culture, stool culture.

Time to abx < 1 hr, choices include Vanco +:

a) cephalosporin 3rd or 4th gen
b) Beta-lactam/beta-lactamase inhibitor (pip/taz, ticar/clav)
c) Carbapenem (imi/mero)
d) If pseudomonas suspected then 2 antipseudomonals used.

Use Early Goal Directed Therapy:

1. ABCs, if necessary intubate
2. ++ fluid boluses, til CVP 8-12, ScvO2 > 70%, urine o/p >0.5cc/kg/hr - crystalloid (NS, RL preferred as initial fluid therapy)
3. Pressors to MAP > 60, start with norepinephrine, then vasopressin
4. transfusion to HCT >0.3
5. Additional therapies: activated protein C, corticosteroids, insulin therapy etc

4. Look for infection as a possible cause in a patient with an ill-defined problem (e.g., confusion in the elderly, failure to thrive, unexplained pain [necrotizing fasciitis, abdominal pain in children with pneumonia]).

5. When a patient returns after an original diagnosis of a simple infection and is deteriorating or not responding to treatment, think about and look for more complex infection. (i.e., When a patient returns complaining they are not getting better, don’t assume the infection is just slow to resolve).

6. When treating infections with antibiotics use other therapies when appropriate (e.g., aggressive fluid resuscitation in septic shock, incision and drainage of abscess, pain relief).

Study Guide



List of Reportable Diseases
CPS Guidelines 2009 on AOM
Antibiotic Spectra Chart
RxFiles 8th edition 2010

Practice SAMP

Infections SAMP