Fatal septic shock due to Capnocytophaga canimorsus bacteremia masquerading as COVID-19 pneumonia - a case report

Capnocytophaga canimorsus (C. canimorsus) infections are rare and usually present with unspecific symptoms, which can eventually end in fatal septic shock and multiorgan failure. The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) related coronavirus disease 2019 (COVID-19), on the other hand, is predominantly characterized by acute respiratory failure, although other organ complications can occur. Both infectious diseases have in common that hyperinflammation with a cytokine storm can occur. While microbial detection of C. canimorsus in blood cultures can take over 48 h, diagnosis of SARS-CoV-2 is facilitated by a widely available rapid antigen diagnostic test (Ag-RDT) the results of which are available within half an hour. These Ag-RDT results are commonly verified by a nucleic acid amplification test (NAAT), whose results are only available after a further 24 h.

A 68-year-old male patient with the diagnosis of COVID-19 pneumonia was referred to our Intensive Care Unit (ICU) from another hospital after testing positive on an Ag-RDT. While the initial therapy was focused on COVID-19, the patient developed a fulminant septic shock within a few hours after admission to the ICU, unresponsive to maximum treatment. SARS-CoV-2 NAATs were negative, but bacteremia of C. canimorsus was diagnosed post-mortem. Further anamnestic information suggest that a small skin injury caused by a dog leash or the subsequent contact of this injury with the patient’s dog could be the possible point of entry for these bacteria.

During the acute phase of hyperinflammation and cytokine storm, laboratory results can resemble both, sepsis of bacterial origin or SARS-CoV-2. This means that even in the light of a global SARS-CoV-2 pandemic, where this diagnosis provides the most salient train of thoughts, differential diagnoses must be considered. Ag-RDT can contribute to early detection of a SARS-CoV-2 infection, but false-positive results may cause fixation errors with severe consequences for patient outcome.