Wound Infection

Surgical Wound Infection: Mycobacterium tuberculosis A case close to the heart

Case #1 A 57-year-old Chinese woman who had undergone Coronary Artery Bypass Grafting (CABG) by median sternotomy for triple-vessel disease 8 months beforehand, presented to the hospital

Patient History

The patient has a history of: • Hypertension

• Hyperlipidemia • Insulin-dependent diabetes mellitus  o Diabetic nephropathy o Continuous

ambulatory peritoneal dialysis (CAPD)

Clinical Symptoms 6 months after surgery developed: • purulent discharge from a nodular lesion over the sternotomy

 

• Two 1 1.5-cm nodular lesions discharging serosangious fluid

 

• Mild erythema over the lower half of sternotomy wound

 

• Fever = 37'C

 

Clinical Syndrome Conditions WBC count

Patient 5900 cells/ mm3

Neutrophils

83.4%

Normal 4,300 -10,800 cells/mm3 33%

Lymphocytes

13.2%

20 – 40%

Monocytes

1%

2 – 8%

Hemoglobin level

8.3 g/dL

12 – 18 g/dL

Platelet count

155 000 cells/mm3 150000 - 450000 cells/ mm3 >130 mm/h 130 mm/h

Erythrocyte sediment rate

Diagnosis Common causative organisms in surgical site infections: • Staphylococcus aureus • Enterobacteriaceae o Escherichia coli and Enterobacter spp. Occasional organisms: • rapidly growing mycobacteria have caused infection of sternum after open heart surgery o Mycobacterium fortuitum o Mycobacterium chelonae Rare organisms: • Mycobacterium tuberculosis

Laboratory Detection • Wound Cultures o Gram Stain o Aerobic and anaerobic bacterial cultures

• Expectorate sputum samples o Gram Stain o Ziehl–Neelsen stain o Aerobic and anaerobic bacterial cultures o Polymerase Chain Reaction (PCR)

Laboratory Results • Wound Cultures o Gram Stain  Gram Positive Cocci (Chains)

o Aerobic and anaerobic bacterial cultures  Positive Growth on both

• Methicillin-sensitive Staphylococcus aureus

Laboratory Results • Expectorate sputum samples: o Gram Stain  Negative Growth

o Ziehl–Neelsen stain  Acid-fast bacilli

o Aerobic and anaerobic bacterial cultures  Negative Growth on Both

Laboratory Results Gram stain •Staphylococcus aureus

http://microvet.arizona.edu/Courses/JCMIC205/S 08/Images/fig2grampos_cocci.jpg

Acid fast Stain • Acid-fast bacilli

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Case #2  An 80 year old female presented an epigastric mass which appeared in Novemeber 2007 and slowly grew over 4 weeks.

She has had two coronary artery bypass grafts performed; The first being in 1998 and the second in 2006.

Patient History The patient has a history of: • Cardiovascular and Valvular disease • Mitral, aortic and tricupsic valve replacement • During the second CABG, in anticipation of a biventricular pacemaker the patient had pacing wires installed • She had migrated from SEA to United States in 1981

Clinical Symptoms • Epigastric mass formation 11 months after CABG •Subcutaneous abscess over the pacemaker site

• Inferior aspect of sternal incision wound • No erythema • No wound dehiscence

Laboratory Detection CT scan revealed fluid collection extending from the sternal cerclage wire into the peritoneum Fluid collection was performed by a needle aspiration which was then tested bacterial cultures Negative for gram stain as well as routine bacterial cultures Debridement of Fluid cavity revealed fibrinous, purulent, abscess surrounding the pacing wires

Laboratory Detection • Needle aspirated fluid collection • Gram strain • Bacterial cultures – Anaerobic and aerobic • Debridement of Fluid cavity • Aerobic and anaerobic bacterial cultures • Acid fast bacilli and fungal cultures • Liquid chromotography

Lab Results Needles aspirated fluid collection Negative for bacteria Debridment of Fluid Cavity Negative for bacteria TB was only considered when AFB cultures grew Mycobacterium Tuberculosis 5 weeks after initial testing. Liquid chromatography was performed as a

About Mycobacterium tuberculosis Acid-fast, non-motile bacilli. Obligate aerobes. Non-spore forming. Very slow growing; divides every 15-20 hours. 1.5-3 μm long Humans = only reservoir

Virulence Factors Factor

Action

Mycolic Acid

Increases resistance.

HBHA

Promotes dissemination and cell binding.

ICL

Mediates intracellular survival.

PGL

Suppresses immune response (only hypervirulent strains).

Epidemiology

Normal TB Symptoms Usually pulmonary; productive prolonged cough, coughing up blood, fever, weight loss. Can progress to extrapulmonary forms EG miliary and meningeal TB. Cutaneous/wound infections are EXTREMELY RARE.

Immune response • Prevents fusion of phagosome with lysosomes. – Avoids being killed by badass proteins.

• APCs secrete IL-12 and TNF-α. – Recruit T cells, NK cells – IFN-γ produced, macrophage activation

• Infection not cleared = tissue necrosis • Infection cleared = granuloma

Lysoso me

Lyso som e

IFNγ

IFNγ

Lysoso me Contains: •Lipase •Carbohydrase •Protease •Nuclease

eitrich & Doherty, 2009)

IFNγ

IFNγ

IFNγ

IFNγ

IFNγ

IFNγ

IFNγ

IFNγ

IFNγ

IFNγ

IFNγ IFNγ IFNγ

IFNγ

IFNγ IFNγ IFNγ

IFNγ IFNγ IFNγ

IFNγ

IFNγ IFNγ

IFNγ IFNγ

IFNγ IFNγ IFNγ

Radiology

57 y/o Chinese woman

80 y/o pacemaker woman

Treatments Antibiotics: • isoniazid (IHD) • rifampin • pyrazinamide • ethambutol • streptomycin Surgical debridement of wound.

Treatment of Case #1 • Initial treatment of Staph. aureas with cloxacillin. • Wound debridement revealed necrosis of xyloid cartilage • Discovery of TB waranted antituberculous chemotherapy: o isoniazid 200 mg daily o pyrazinamide 1 g daily o ethambutol 1000 mg 3 times per week o levofloxacin 500 mg 3 times per week

Treatment of Case #2 • She was initially treated daily with: o isoniazid (INH) 300 mg o rifampicin 450 mg o ethambutol 800 mg • Switched after 16 weeks to INH 900 mg and rifapentine 600 mg weekly. • Pyrazinamide was excluded.

Sources of Infection • In both cases patients were from TB endemic areas, but had no history of TB infection. • Surgery may have re-activated latent infection • Equipment may have been contaminated • Medical staff may have been infected (not likely) Implications • Pyrazinamide prophylaxis?

Outcome of Patients 1. The patient received 3 months of antituberculous treatment and showed no evidence of relapse. 2. She responded well to treatment and has completed 25 of 39 weeks of DOT.

Before

After

References