From the Guidelines
The diagnosis of infective endocarditis relies on the modified Duke criteria, which includes major and minor criteria, as outlined in the most recent guidelines from 2015 1. The major criteria consist of positive blood cultures (at least two separate cultures showing typical organisms like Streptococcus viridans, Streptococcus bovis, HACEK group, Staphylococcus aureus, or community-acquired enterococci) and evidence of endocardial involvement (echocardiogram showing a vegetation, abscess, or new valvular regurgitation). Some key points to consider when applying these criteria include:
- The importance of blood culture results, with at least two separate cultures showing typical organisms, as noted in the 2015 guidelines 1
- The role of echocardiography in demonstrating evidence of endocardial involvement, as discussed in the 2005 study 2
- The consideration of minor criteria, such as predisposing heart conditions, fever, and vascular phenomena, as outlined in the 2009 guidelines 3 Minor criteria include:
- Predisposing heart conditions or intravenous drug use
- Fever above 38°C (100.4°F)
- Vascular phenomena (arterial emboli, septic pulmonary infarcts, mycotic aneurysm, intracranial hemorrhage, conjunctival hemorrhages, or Janeway lesions)
- Immunologic phenomena (glomerulonephritis, Osler's nodes, Roth spots, or rheumatoid factor)
- Microbiological evidence not meeting major criteria A definite diagnosis requires either 2 major criteria, 1 major and 3 minor criteria, or 5 minor criteria, as stated in the 2015 guidelines 1. Possible endocarditis is diagnosed with 1 major and 1 minor criterion or 3 minor criteria. These criteria help clinicians systematically evaluate patients with suspected endocarditis, though clinical judgment remains essential as some cases may not fulfill these criteria despite having the disease, as noted in the 2005 study 2 and the 2013 report 4.
From the Research
Major and Minor Criteria for Infective Endocarditis
The diagnosis of infective endocarditis (IE) is based on a combination of clinical, microbiological, and echocardiographic findings. The modified Duke criteria are widely used for the diagnosis of IE, which include major and minor criteria 5. The major criteria are:
- Typical blood culture (e.g., Streptococcus viridans, Staphylococcus aureus)
- Positive echocardiogram (e.g., vegetation, abscess, new partial dehiscence of prosthetic valve) The minor criteria are:
- Predisposition (e.g., heart condition, intravenous drug use)
- Fever
- Vascular phenomena (e.g., emboli, Janeway lesions)
- Immunologic phenomena (e.g., glomerulonephritis, rheumatoid factor)
- Suggestive echocardiogram (e.g., thickened valve, prosthetic valve)
- Suggestive microbiologic findings (e.g., positive blood culture but not typical for IE)
Application of the Duke Criteria
The Duke criteria have been shown to be more sensitive and specific than older criteria for the diagnosis of IE 5, 6. A study of 405 consecutive cases of suspected IE found that the new criteria increased the number of definite diagnoses and reduced the number of rejected cases 5. Another study of 93 patients with pathologically proven IE found that the Duke criteria had a sensitivity of 76% compared to 56% for the von Reyn criteria 6.
Limitations of the Duke Criteria
Despite the improved sensitivity and specificity of the Duke criteria, there are still limitations to their use. A study of 241 patients with suspected IE found that 24% of patients with proven IE remained misclassified as "possible IE" despite the use of Duke criteria 7, 6. This was often due to negative blood cultures or Q-fever endocarditis diagnosed by positive serology. The study suggested that increasing the diagnostic value of echographic criteria and considering serologic diagnosis of Q fever as a major criterion could further improve the clinical diagnosis of IE 6.