Answer to October 2015 Photo Quiz

Abstract

Answer: Streptococcus pyogenes. Figure 1 in the photo quiz demonstrates hypergranular, vacuolated neutrophils with intracellular cocci forming chains, resembling the genus Streptococcus. In light of the clinical features and blood film, a presumptive diagnosis of Streptococcus pyogenes toxic shock syndrome was made. Six hours following the blood film observation, growth of Gram-positive cocci in chains was detected in blood culture, which was subsequently confirmed to be S. pyogenes. As a result of the blood film findings, intravenous clindamycin was added; however, 19 h after presentation, the patient died of multiorgan failure. The published literature suggests that observation of bacteria on routine blood film is rare; case reports involving Capnocytophaga canimorsus (1), Citrobacter koseri (2), and Streptococcus pneumoniae (3) have been described, plus a case series of four neonates involving Staphylococcus aureus and coagulase-negative staphylococci (4). A larger case series, published in 1966, reported 26 bacteremic patients with bacteria observed within leukocytes on routine blood films (S. aureus, S. pneumoniae, Escherichia coli, Klebsiella pneumoniae, Neisseria meningitidis, Proteus species, viridans group Streptococcus, beta-hemolytic Streptococcus, and “paracolon bacillus”) (5). To the best of our knowledge, this is the first case of S. pyogenes observed in a routine blood film. The high fatality rate among these published cases (24 of 33 patients died) (1,–5) likely reflects the poor diagnostic sensitivity of blood films except in patients with very high bacterial loads observed during overwhelming septicemia, such as in our case. The use of buffy-coat smears may improve sensitivity (to a limit of detection of 104 CFU/ml) but is labor- and time-consuming, prohibiting its routine use (6). Bacteria observed during routine blood film examination should be discussed immediately with the treating physician, as the result may be used to predict a microbiological diagnosis and assist with choice of empirical antimicrobial and adjunctive therapy and portends a poor patient outcome. (See page 3109 in this issue [doi:10.1128/JCM.02824-13] for photo quiz case presentation.)