Uncomplicated Vs. Complicated Staph Aureus Bacteremia

Uncomplicated Staph Aureus Bacteremia 

  • No evidence of endocarditis
  • No prosthetic device
  • No evidence of metastatic infection
  • Defervescence after 72 hours of active antibiotic treatment
  • Negative blood cultures at 48-96 hours
  • Antibiotics for 14 days

Complicated Staph Aureus Bacteremia

  • Endocarditis
  • Prosthetic device (i.e. pacemaker, prosthetic joint, hemodialysis line)
  • Evidence of metastatic infection (abscess, vertebral osteomyelitis, etc.)
  • Persistent bacteremia, despite 3 or more days of antibiotic treatment
  • Antibiotics for 4-6 weeks

Treatment options for Staph Aureus: 

  • Vancomycin, if intolerant: Daptomycin +/- Cloxacillin
  • If MSSA, can use Cloxacillin
  • If MRSA, use Vancomycin

REFERENCES

Jr, V. G. (2003, September 22). Clinical Identifiers of Complicated Staphylococcus aureus Bacteremia. Retrieved from https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/216060

Susceptibility to Vancomycin: E. faecium & E. faecalis

Vancomycin-resistant enterococci (VRE) first appeared in Europe during the 1980s. It rapidly spread to North America by the 1990s. 

Susceptibility:

More than 50% of E. faecium in the United States are VRE.

E. faecalis tends to be susceptible to vancomycin.

Most frequent form of VRE infection: UTI, followed by catheter line associated bacteremia (i.e hemodialysis, central lines).

Treatment for VRE: daptomycin, linezolid, and tigecycline. Susceptible strains may be treated with ampicillin.

REFERENCES:

  1. Principles and Practice of Hospital Medicine, 2e. Chapter 185: Antibiotic Resistance. L. Silvia Munoz-Price.

Animal Bites: Pasteurella, Capnocytophaga, Eikenella

A common infectious disease question is what organism(s) is associated with different kinds of bites.

Cat Bites: Pasteurella multocida

Dog Bites: Capnocytophaga canimorsus

Human Bites: Eikenella corrodens

REFERENCES

  1. Janda JM, Graves MH, Lindquist D, Probert WS. Diagnosing Capnocytophaga canimorsus Infections. Emerging Infectious Diseases. 2006;12(2):340-342. 
  2. Patil PD, Panchabhai TS, Galwankar SC. Managing human bites. Journal of Emergencies, Trauma and Shock. 2009;2(3):186-190. doi:10.4103/0974-2700.55331.
  3. Arons MS, Fernando L, Polayes IM. Pasteurella multocida–the major cause of hand infections following domestic animal bites. J Hand Surg Am. 1982 Jan;7(1):47-52.

Piperacillin-tazobactam induced hypokalemia: Mechanism

Piperacillin/tazobactam is a commonly used antibiotic with tolerable side effects and broad antimicrobial activity in general practice.

Rare side-effects can include hypokalemia.
WHY? Two theories exist:

  1. Piperacillin-sodium is a negatively charged molecule (anion) and nonabsorbable. This increases transepithelial electronegativity in the distal nephron, increasing  potassium (cation) excretion. (-) draws out the (+)
  2. The large volume of sodium administered with Piperacillin-tazobactam can result in solute diuresis.

REFERENCES

  1. Hussain S, Syed S, Baloch K. Electrolytes imbalance: a rare side effect of piperacillin/ tazobactam therapy. J Coll Physicians Surg Pak. 2010;20(6):419-420.
  2. Zaki SA, Lad V. Piperacillin-tazobactam-induced hypokalemia and metabolic alkalosis. Indian Journal of Pharmacology. 2011;43(5):609-610. doi:10.4103/0253-7613.84986.
  3. Polderman KH, Girbes AR. Piperacillin-induced magnesium and potassium loss in intensive care unit patients. Intensive Care Med. 2002;28(4):520-522.c

What is Fat Stranding?

Fat stranding is a term used to describe increased (abnormal) attenuation of fat on CT scan typically. It is suggestive of inflammation causing edematous changes and lymphatic engorgement.

REFERENCES

  1. Zalcman M, Sy M, Donckier V, Closset J, Gansbeke DV. Helical CT signs in the diagnosis of intestinal ischemia in small-bowel obstruction. AJR 2000 ; 175:1601–1607.
  2. Thornton E, Mendiratta-Lala M, Siewert B, Eisenberg RL (2011) Patterns of fat stranding. Am J Roentgenol 197:W1–W14
  3. Jose M. Pereira, Claude B. Sirlin, Pedro S. Pinto, R. Brooke Jeffrey, Damien L. Stella, and Giovanna Casola. Disproportionate Fat Stranding: A Helpful CT Sign in Patients with Acute Abdominal Pain. RadioGraphics 2004 24:3, 703-715 

C5-C9 Deficiency: Neisseria infections

Neisseria meningitidis (Gram-negative cocci) life threatening cause of Membrane_Attack_Complex_(Terminal_Complement_Complex_C5b-9)sepsis and bacterial meningitis.

Classically, individuals who lack terminal complement proteins (C5-C9) cannot form the membrane attack complex (MAC), which is needed for bacterial lysis of this encapsulated pathogen (can lead to a 1000- to 10,000-fold increased risk of meningococcal disease). More information here.

REFERENCES

  1. Figueroa, J.E., and P. Densen. 1991. Infectious diseases associated with complement deficiencies. Clin. Microbiol. Rev. 4:359–395.
  2. Infectious diseases associated with complement deficiencies. Figueroa JE, Densen P. Clin Microbiol Rev. 1991 Jul; 4(3):359-95.
  3. Rosa D.D., Pasqualotto A.C., de Quadros M., Prezzi S.H. Deficiency of the eighth component of complement associated with recurrent meningococcal meningitis—case report and literature review. Braz J Infect Dis. 2004;8(August (4)):328–330.

When to Treat Asymptomatic Bacteriuria?

Asymptomatic Bacteriuria can be defined as a positive urine culture (Two consecutive clean-catch voided urine specimens of at least 100,000 CFUs/mL in women and 1 clean-catch in men/ Catheterized patients) in the absence of any symptoms (i.e fever, frequency, urgency, supra-pubic pain). In particular patient populations, asymptomatic bacteriuria should be treated:

  1. Pregnant Women
  2. Renal transplant recipient
  3. Patient undergoing invasive urologic procedure (in which mucosal bleeding is anticipated)

REFERENCES

  1. Colgan R, Nicolle LE, McGlone A, Hooton TM. Asymptomatic bacteriuria in adults. Am Fam Physician. 2006 Sep 15;74(6):985-90.
  2. Nicolle LE, Bradley S, Colgan R, Rice JC, Schaeffer A, Hooton TM, Infectious Diseases Society of America, American Society of Nephrology, American Geriatric Society. Infectious Diseases Society of America guidelines for the diagnosis and treatment of asymptomatic bacteriuria in adults. Clin Infect Dis. 2005;40(5):643.  
  3. Lin K, Fajardo K, U.S. Preventive Services Task Force. Screening for asymptomatic bacteriuria in adults: evidence for the U.S. Preventive Services Task Force reaffirmation recommendation statement. Ann Intern Med. 2008;149(1):W20.  

Antibiotics and Enterohemorrhagic Escherichia coli (EHEC) Diarrhea

Controversy surrounds the use of antibiotics in the treatment of enterohemorrhagic Escherichia coli (EHEC) infections due to concerns about triggering hemolytic-uremic syndrome (HUS). The most common EHEC serotype causing human diseases worldwide is O157:H7.

Antibiotic therapy is generally NOT beneficial or recommended in patients with EHEC infection (particularly in children <10 years).

WHY? Several studies have shown increased induction of Shiga toxin with antibiotic therapy (i.e fluoroquinolones, trimethoprim-sulfamethoxazole, ampicillin). Shiga toxin is the major virulence factor of EHEC involved in the pathogenesis of HUS.

REFERENCES

  1.  Holtz LR, Neill MA, Tarr PI  . 2009. Acute bloody diarrhea: a medical emergency for patients of all ages. Gastroenterology 136:1887–1898.
  2. Smith KE, et al  . 2012. Antibiotic treatment of Escherichia coli O157 infection and the risk of hemolytic uremic syndrome, Minnesota. Pediatr. Infect. Dis. J. 31:37–41.
  3. Tarr PI, Gordon CA, Chandler WL . 2005. Shiga-toxin-producing Escherichia coli and haemolytic uraemic syndrome. Lancet 365:1073–1086. 
  4. Wong CS, Jelacic S, Habeeb RL, Watkins SL, Tarr PI  . 2000. The risk of the hemolytic-uremic syndrome after antibiotic treatment of Escherichia coli O157:H7 infections. N. Engl. J. Med. 342:1930–1936.
  5.  Buchholz U, et al  . 2011. German outbreak of Escherichia coli O104:H4 associated with sprouts. N. Engl. J. Med. 365:1763–1770.
  6. Bielaszewska, Martina et al.  Effects of Antibiotics on Shiga Toxin 2 Production and Bacteriophage Induction by Epidemic Escherichia coli O104:H4 Strain. Antimicrob. Agents Chemother. June 2012 vol. 56 no. 6 3277-3282.
  7. Wong, C.S. et al. Risk factors for the hemolytic uremic syndrome in children infected with Escherichia coli O157:H7: a multivariable analysis. Clin Infect Dis. 2012;55(1):33. 

What is the Jarisch-Herxheimer reaction?

The Jarisch-Herxheimer reaction is commonly seen in the first 24 hours of treatment and is characterized by low-grade fever, chills, headache, myalgias, malaise, and skin lesions (new or worsening of preexisting).

WHY? Thought to be due to cytokine release in response to endotoxins released by the dying microorganisms. May be seen following the treatment of  spirochetal illnesses ( eg, Lyme disease, Syphilis, Leptospirosis).

*Typically treated with antipyretics.

REFERENCES

  1. FARMER TW. JARISCH-HERXHEIMER REACTION IN EARLY SYPHILIS. JAMA. 1948;138(7):480-485. doi:10.1001/jama.1948.02900070012003
  2. Pound MW, May DB. Proposed mechanisms and preventative options of Jarisch-Herxheimer reactions. J Clin Pharm Ther 2005;30:291-295.

Urine Dipstick: Nitrates and Nitrites

On an urine dipstick for suspected UTI, it is not uncommon to find positive nitrites. Nitrates are normally excreted by the kidney, however nitrites are not normally found in urine. Nitrites will be found when nitrate reductase organisms are present in the molecular-structure-of-nitrates-and-nitritespatient’s urine. These organisms are gram-negative bacteria including E. coli and other bacteria in the family Enterobacteriaceae (i.e Klebsiella).

NOTE: However, several other common urinary pathogens do not produce nitrites, such as: enterococci, S. saprophyticus, and Pseudomonas!! Therefore negative nitrites DOES NOT RULE OUT BACTERIURIA.

WATCH OUT FOR FALSE (-):

  1. If a patient has insufficient nitrates (i.e low vegetable intake in their diet), there may not be sufficient material to be converted by the bacteria
  2. It takes at least 4 hours for bacteria to convert nitrates to detectable levels of nitrite, so this test may be negative in patients with UTIs whose urinary frequency does not provide adequate time for bacterial conversion of nitrates to nitrites

REFERENCES

  1. Simerville JA, Maxted WC, Pahira JJ. Urinalysis: a comprehensive review. Am Fam Physician. 2005 Mar 15;71(6):1153-62.
  2. Chapter 104. Urinalysis and Urine Electrolytes. Principles and Practice of Hospital Medicine. dam C. Schaffer, MD