My patient with pyelonephritis has positive blood cultures for E. coli? Should I order repeat blood cultures to make sure the bacteremia is clearing?

Although a common practice, follow-up blood cultures (FUBCs) may not be necessary in otherwise clinically stable or improving patients with aerobic gram-negative bacteremia. This is probably due to the often-transient nature of gram-negative bloodstream infections  and less propensity of these organisms to cause intravascular infections (eg, endocarditis) compared to gram-positives. 1

A 2017 study addressing the value of FUBCs in gram-negative bacteremia found that repeat positive blood cultures were uncommon with positive results not associated with mortality or higher ICU admissions. 1 Specifically, 17 FUBCs had to be drawn to yield 1 positive result.  Although the numbers of positive FUBCs were too low for in-depth analysis, it was concluded that FUBCs added little value in the management of gram-negative bacteremias.

In contrast, FUBCs are recommended in the following situations: 1-3

  • Staphylocccus aureus bacteremia given the propensity of this organism to cause intravascular (eg, endocarditis) and metastatic infections.
  • Presumed or documented endocarditis or intravascular device infections (eg, intravenous catheters and pacemakers) to document timely clearance of bacteremia
  • Infections involving organisms that may be difficult to clear such as fungemia or multi-drug resistant pathogens.

As with many things in medicine, clinical context is important before ordering tests and blood cultures are no different. The urge to order FUBCs should also be balanced with the possibility of having to deal with  contaminants. 

References

  1. Canzoneri CN, Akhavan BJ, Tosur Z et al. Follow-up blood cultures in gram-negative bacteremia: Are they needed? Clin Infect Dis 2017;65:1776-9. https://www.ncbi.nlm.nih.gov/pubmed/29020307
  2. Tabriz MS, Riederer K, Baran J, et al. Repeating blood cultures during hospital stay: Practice pattern at a teaching hospital and a proposal for guidelines. Clin Microbiol Infect 2004;10:624-27. https://onlinelibrary.wiley.com/doi/full/10.1111/j.1469-0691.2004.00893.x
  3. Mylotte JM, Tayara A. Blood cultures: Clinical aspects and controversies. Eur J Clin Microbiol Infect Dis 200;19:157-63. https://www.ncbi.nlm.nih.gov/pubmed/10795587

 

 

My patient with pyelonephritis has positive blood cultures for E. coli? Should I order repeat blood cultures to make sure the bacteremia is clearing?

My patient just developed a fixed drug reaction from ibuprofen. What is the mechanism of this type of skin reaction?

Although its mechanism is not full elucidated, fixed drug eruption (FDE) is thought to result from the drug-induced cytotoxic activation of CD8+ memory T cells.1 ,2

In this context, the culprit medication behaves as a hapten that adheres to basal keratinocytes which in turn results in the recruitment of T cells and inflammation.  However, as the inflammation resolves, CD8+  effector-memory T cells remain in the area in question,  setting the stage for more rapid immunologic reaction when the drug is reintroduced.

Why a systemic drug triggers a reaction only at specific sites in the body is a fascinating question. Prior herpes simplex virus (HSV) infection (eg, on the lips or genitalia) may explain some cases.1 Interestingly, despite the absence of prior herpetic lesions, most patients with FDE are seropositive for HSV. Previously traumatized body sites (e.g. from burns or insect bites) may also create an immune microenvironment conducive to FDE.

The classic presentation of FDE is reappearance of a rash in the genitals, perianal areas, hands, and feet within 30 min to 8 hours of taking the culprit medication.3 Look specifically for NSAIDs, tetracyclines, sulfonamides, and aspirin on the patient’s drug list. 4

References

  1. Shiohara, T. Fixed drug eruption: Pathogenesis and diagnostic tests. Curr Opin Allergy Clin Immunol 2009; 9:316-21. https://www.ncbi.nlm.nih.gov/pubmed/19474709
  2. Butler, DF. Fixed Drug Eruptions. Medscape. http://emedicine.medscape.com/article/1336702-overview#a4. Accessed March 26, 2018.
  3. Korkij W, Soltani K. Fixed drug eruptions: A brief review. Arch Dermatol 1984;120:520. https://www.ncbi.nlm.nih.gov/pubmed/6231004
  4. Oakley, A. Fixed Drug Eruption. https://www.dermnetnz.org/topics/fixed-drug-eruption Accessed March 26, 2018.

 

Contributed by Amir Hossein Ameri, Medical Student, Harvard Medical School

My patient just developed a fixed drug reaction from ibuprofen. What is the mechanism of this type of skin reaction?

How accurate are peripheral thermometers for estimating body temperature in my patient with chills?

Though convenient, oral, tympanic membrane, axillary, and temporal artery thermometers (AKA “peripheral thermometers”) may not be highly accurate in measuring body temperature.

A 2015 systematic review and meta-analysis of the performance of peripheral thermometers involving 75 studies (mostly in adults) found that compared to central thermometers (eg, pulmonary artery, urinary bladder, rectal), peripheral thermometers had a low sensitivity (64%, 95% CI 55%-72%), but much better specificity (96%, 95% CI 93%-97%) for fever (most commonly defined as 37.8° C [100° F] or greater).1

In the same study, for oral electronic thermometers, sensitivity was 74% with a specificity of 86%. For temporal artery thermometers, sensitivities ranged from 26% to 91%, while specificities ranged from 67% to 100%. For tympanic membrane thermometers, sensitivities ranged from 23% to 87%, with a specificity of 57% to 99%.

A 2016 study involving adult emergency department patients reported the sensitivity of peripheral thermometers (vs rectal temperature 38 C [100.4] or higher) as follows: oral (37%), tympanic membrane (68%), and temporal artery (71%). Specificity for fever was >90% for all peripheral thermometers. 2

So, it looks like while we may be pretty comfortable with a diagnosis of “fever” when our patient with chills has a high temperature recorded by a peripheral thermometer, lack of fever alone by these devices should not veer us away from the possibility of systemic infection. When in doubt and if possible, check a rectal temperature.

References

  1. Niven DJ, Gaudet JE, Laupland KB. Accuracy of peripheral thermometers for estimating temperature: A systematic and meta-analysis. Ann Intern Med 2015;163:768-777. https://www.ncbi.nlm.nih.gov/pubmed/26571241
  2. Bijur PE, Shah PD, Esses D. Temperature measurement in the adult emergency department: oral tympanic membrane and temporal artery temperatures versus rectal temperature. Emerg Med J 2016;33:843-7. https://www.ncbi.nlm.nih.gov/pubmed/27334759

 

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How accurate are peripheral thermometers for estimating body temperature in my patient with chills?

My elderly nursing home patient is admitted with recent poor oral intake, falls and oral temperatures of 99.1°-99.3° F(37.3°-37.4°C). Is she considered febrile at these temperatures?

Yes! Even though we often think of temperatures of 100.4°F (38° C) or greater as fever, older people often fail to mount an appropriate febrile response despite having a serious infection. 1

Infectious Diseases Society of America (IDSA) guideline on evaluation of fever in older adult residents of long-term care facilities has defined fever in this population as:2

  • Single oral temperature >100° F (>37.8° C) OR
  • Repeated oral temperatures >99° F (>37.2° C) OR
  • Rectal temperatures >99.5° F (>37.5° C) OR
  • Increase in temperature of >2° F (>1.1° C) over the baseline temperature

Even at these lower than traditional thresholds for defining fever, remember that many infected elderly patients may still lack fever. In a study involving bacteremic patients, nearly 40% of those 80 years of age or older did not have fever (defined as maximum temperature over 24 hrs 100° F [37.8°C] or greater).3  

So our patient meets the criteria for fever as suggested by IDSA guidelines and, particularly in light of her recent poor intake and falls, may need evaluation for a systemic source of infection.

Now that’s interesting! Did you know that blunted febrile response of the aged to infections may be related to the inability of cytokines (eg, IL-1) to reach the central nervous system?1

References 

  1. Norman DC. Fever in the elderly. Clin Infect Dis 2000;31:148-51. https://academic.oup.com/cid/article/31/1/148/318030
  2. High KP, Bradley SF, Gravenstein S, et al. Clinical practice guidelines for the evaluation of fever and infection in older adult residents of long-term care facilities: 2008 update by the Infectious Disease Society of America. Clin Infect Dis 2009;48:149-71. http://www.idsociety.org/uploadedFiles/IDSA/Guidelines-Patient_Care/PDF_Library/Fever%20and%20Long%20Term%20Care.pdf
  3. Manian FA. Fever, abnormal white blood cell count, neutrophilia, and elevated serum C-reactive protein in adult hospitalized patients with bacteremia. South Med J 2012;105;474-78. http://europepmc.org/abstract/med/22948327
My elderly nursing home patient is admitted with recent poor oral intake, falls and oral temperatures of 99.1°-99.3° F(37.3°-37.4°C). Is she considered febrile at these temperatures?

My patient with COPD has new clubbing of his finger tips. What is the mechanism of clubbing?

The mechanism behind digital clubbing has yet to be fully elucidated, with hypotheses ranging from a circulating vasodilator, tissue hypoxia, a neurocirculatory reflex, and genetic factors. 1 Although hypoxemia is often cited as a cause of clubbing, it is often absent in the presence of clubbing and many patients with hypoxemia do not have clubbing.

A potentially unifying pathophysiologic mechanism of clubbing revolves around platelet clustering and associated growth factor release. 2.3 Platelet clumps/megakaryocytes—either because of circumvention of the lung capillary network (eg, in intracardiac shunts or lung cancer) or increased production (eg, in left-sided endocarditis or chronic inflammatory conditions)—may wedge in the fine vasculature of distal fingertips or toes and cause release of platelet-derived growth factor (PDGF) and vascular endothelial growth factor (VEGF).

Together, PDGF and VEGF promote neovascularization, increase vessel dilation and permeability, and modify connective tissue to create the distinct club-like appearance. Local hypoxic condition from reduced capillary perfusion is thought to further stimulate the release of these growth factors.

Potential causes of clubbing in our patient include lung cancer, interstitial lung disease, bronchiectasis, core pulmonale and secondary polycythemia, among many others. 1

Fun Fact: Did you know that clubbing, also known as “Hippocratic finger”, was first described by Hippocrates in a patient with chronic empyema (don’t ask how chronic empyema was diagnosed in 400 BC!)?1

 

References

  1. McPhee SJ. Clubbing. In: Walker HK, Hall WD, Hurst JW, editors. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition. Boston: Butterworths;1990. Chapter 44. Available from https://www.ncbi.nlm.nih.gov/books/NBK366/
  2. Dickinson CJ, Martin JF. Megakaryocytes and platelet clumps as the cause of finger clubbing. Lancet 1987;2:1434-4. https://www.ncbi.nlm.nih.gov/pubmed/2891996/ 
  3. Atkinson S, Fox SB. Vascular endothelial growth factor (VEGF)-A and platelet-derived growth factor (PDGF) play a central role in the pathogenesis of digital clubbing. J Pathol 2004;203:721-8. https://www.ncbi.nlm.nih.gov/pubmed/15141388

 

Contributed by George Bugarinovic, Medical Student, Harvard Medical School

My patient with COPD has new clubbing of his finger tips. What is the mechanism of clubbing?

Does my patient about to undergo immunosuppressive therapy need antiviral prophylaxis even if she tests positive for hepatitis B surface antibody?

The presence of hepatitis B surface antibody (HBsab) in patients who also test positive for core antibody does not necessarily confer full protection against hepatitis B virus (HBV) reactivation during immunosuppression (incidence 4.3%). 1 This is because despite having HBsab and no HB surface antigen,  a small portion of patients continue to have detectable HBV DNA in the serum and are therefore at risk of reactivation during severe immunosuppression. 2

In fact, the American Gastroenterological Association recommends against using anti-HBs status to guide antiviral prophylaxis in anti-HBc-positive patients. 1

Overall, antiviral prophylaxis may reduce the risk of HBV reactivation by 87% (C.I. 70%-94%). Antiviral drugs with a high barrier to resistance (eg, entecavir) are preferred over lamivudine.

Immunosuppressants often requiring HBV prophylaxis include: 1-3

  • B cell-depleting agents (eg, rituximab, ofatumumab)
  • Anthracycline derivatives (eg, doxorubicin, epirubicin)
  • Prednisone (4 weeks or more)
  • Tumor necrosis factor inhibitors (eg, etanercept, adalimumab, certolizumab, infliximab)
  • Other cytokine or integrin inhibitors (eg, abatacept, ustekinumab, natalizumab, vedolizumab)

Traditional immunosuppressive agents such as azathioprine, 6-mercaptopurine and methotrexate are often considered “low-risk” and do not generally require prophylaxis. 1

Fun Fact: Did you know that hepatitis B virus is very old and probably originated in birds when dinosaurs roamed the earth? 4

References

  1. Reddy KR, Beavers KL, Hammond SP, et al. American Gastroenterological Association Institute Guideline on the prevention and treatment of hepatitis B virus reactivation during immunosuppressive drug therapy. Gastroenterology 2015;148:215-19. https://www.ncbi.nlm.nih.gov/pubmed/25447850
  2. Gigi E, Georgiou T, Mougiou D, et al. Hepatitis B reactivation in a patient with rheumatoid arthritis with antibodies to hepatitis B surface antigen treated with rituximab. HIPPOKATRIA 2013;17:91-93. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3738290/
  3. Kim EB, Kim DS, Park SJ, et al. Hepatitis B virus reactivation in a surface antigen-negative and antibody-positive patient after rituximab plus CHOP chemotherapy. Cancer Res Treat 2008;40:36-38. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2699087/
  4. Suh A, Brosius J, Schmitz J, et al. The genome of a Mesozoic paleovirus reveals the evolution of hepatitis B virus. Nature Communications 2013; Article no. 1791. http://www.nature.com/articles/ncomms2798
Does my patient about to undergo immunosuppressive therapy need antiviral prophylaxis even if she tests positive for hepatitis B surface antibody?

Can my patient contract influenza more than once in a season?

It’s not common but reinfection with influenza can definitely occur, either due to the same viral strain, or due to a different one altogether.

One study reported influenza reinfection due to H1N1 in otherwise healthy patients within 12-20 days of the original infection after an apparent period of full recovery. 1 There was no evidence of resistance to oseltamivir among isolates and all patients recovered after the second infection.

Reinfection with the same viral strain within 2-3 weeks of the initial bout of influenza shouldn’t be too surprising since it takes 4-7 weeks for antibody response to the infection to peak. 2 Reexposure to the same circulating strain of influenza virus (the season can last 6 weeks or longer) can then result in reinfection when the body hasn’t had enough time to make significant amount of protective antibodies following the first infection.

Another explanation is that more than 1 strains of influenza virus often circulate during any given season.   This places patients at risk of infection due to strains of influenza virus that do not confer significant cross-immunity between each other,  resulting in getting “the flu twice in 1 season.” 3

References

  1. Perz CM, Ferres M, Labarca JA. Pandemic (H1N1) 2009 reinfection, Chile. Emerg Infect Dis 2010;16:156-57. https://wwwnc.cdc.gov/eid/article/16/1/pdfs/09-1420.pdf
  2. Treanor JJ. Influenza viruses, including avian influenza and swine influenza. In: Mandell GL, Bennett JE, Dolin R, eds. Principles and practice of infectious diseases. 7th ed. New York: Elsevier; 2010. p 2265-2293.
  3. Rettner R. Can you get the flu twice in 1 season? Scientific American, LiveScience, February 4, 2018. https://www.scientificamerican.com/article/can-you-get-the-flu-twice-in-1-season/ . Accessed February 5, 2018.

 

Can my patient contract influenza more than once in a season?