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Worth a careful look at the blood film

Published:December 30, 2019DOI:https://doi.org/10.1016/j.ejim.2019.12.028

      Keywords

      1. Case description

      A 46-year-old man with a history of alcohol abuse came to the emergency department with fever and a purpuric rash. He had been bitten by a dog on the left hand 3 days earlier. Minimal bleeding occurred, and with the help of the dog's owner the wound was cleansed. The dog had up-to-date immunisations and the bite occurred after the patient provoked the attack. The next day he started having fever, rigors, myalgia, and purple spots on the extremities.
      Physical examination showed irregular, scattered petechiae on his arms and legs (Fig. 1Α). Blood pressure was 100/50 mmHg, temperature 39 °C, and pulse 120 bpm. There was a healing scar with no evidence of erythema or pain at the wound site. He had marked leucocytosis (29×109/L; neutrophils 80%), thrombocytopenia (30×109/L), INR 1.7 (0.8–1.2), and partial-thromboplastin time 55 s (26–39). A peripheral-blood film was examined and found to show 28% band forms, schistocytes, and long, thin, fusiform rods (Fig. 1B), often arranged in end-to-end pairs (Fig. 1C) inside neutrophils. Gram's staining identified these rods as gram-negative bacilli.
      Fig 1
      Fig. 1Clinical findings and blood-film abnormalities. (A) Rash shortly after admission. (B) Peripheral blood film on admission showing vacuolated neutrophils, some of which contain slender fusiform bacilli (arrows), thrombocytopenia, and sporadic fragmented erythrocytes or schistocytes (arrowheads). (C) Bacilli arranged in end-to-end pairs (arrow). The left-shifted blood picture is consistent with a leukaemoid reaction.

      2. What is your diagnosis?

      Capnocytophaga canimorsus (DF-2) sepsis.

      3. Discussion

      Dog bites constitute an important problem. Although 80% of patients never seek and do not need medical help, awareness of bite-related infections is important. The infections may be caused by a variety of aerobes, anaerobes, and facultative anaerobes. Pasteurella multocida is the classic pathogen in dog bites. This gram-negative coccobacillus is well known for causing aggressive localised infections [
      • Morgan M.
      • Palmer J.
      Dog bites.
      ]. Although P. multocida can cause septicaemia, such an overwhelming manifestation would be unusual.
      The clinical presentation of this fulminant illness in an alcoholic person after a dog bite, combined with the presence of organisms with this morphologic pattern, is highly suggestive of Capnocytophaga canimorsus septicaemia.
      Dog and, occasionally, cat bites risk exposure to oral-cavity commensal microorganisms such as C. canimorsus. C. canimorsus causes fulminant infection characterised by purpuric lesions resembling meningococcaemia, particularly in alcoholic, asplenic, or immunocompromised individuals [
      • Morgan M.
      • Palmer J.
      Dog bites.
      ,
      • Janda M.J.
      Capnocytophaga.
      ,
      • Kullberg B.J.
      • Westendorp R.G.
      • van't Wout J.W.
      • Meinders A.E
      Purpura fulminans and symmetrical gangrene caused by capnocytophaga Canimorsus (formerly DF-2) septicaemia—a complication of dog bite.
      ]. Diagnosis can be difficult because this slow-growing organism is so difficult to isolate on blood culture [
      • Janda M.J.
      Capnocytophaga.
      ]. The detection of organisms on the blood film was the simple but critical confirming diagnostic test in this patient.
      Amoxicillin-clavulanic acid and cefotaxime were started. Blood cultures yielded a fastidious gram-negative bacterium subsequently identified as C. canimorsus. Disseminated intravascular coagulation and renal insufficiency complicated his course, but after a protracted hospital stay he recovered adequately to return home.
      Modern technology has revolutionised medical diagnosis, but in some cases of purpuric sepsis a careful look at the blood film may establish the diagnosis more promptly than is possible by any other means—a conclusion worth emphasizing.

      Funding source

      None

      Declaration of Competing Interest

      None

      References

        • Morgan M.
        • Palmer J.
        Dog bites.
        BMJ. 2007; 334: 413-417
        • Janda M.J.
        Capnocytophaga.
        in: Bennett JE Dolin R Blaser MJ Mandell, Douglas, and Bennett's principles and practice of infectious diseases. 6th edition. Elsevier, Philadelphia, PA2015: 2645-2648
        • Kullberg B.J.
        • Westendorp R.G.
        • van't Wout J.W.
        • Meinders A.E
        Purpura fulminans and symmetrical gangrene caused by capnocytophaga Canimorsus (formerly DF-2) septicaemia—a complication of dog bite.
        Medicine (Baltimore). 1991; 70: 287-291