Discussion
This report highlighted the fact that S. warneri , which has not been recognized frequently as a significant human pathogen, caused IE in an elderly patient who had mitral valve regurgitation, which had been followed-up conservatively for 25 years without medical device. Furthermore, the S. warneri IE ran a severe course, such as development of disseminated lesions in the skin, brain, and spine.
Two important clinical issues arose from the clinical course of the present patient. First, S. warneri can cause IE in a patient with valvular heart disease without medical device. Second, S. warneriIE can run a severe course, such as development of disseminated lesions, in an elderly patient.
First, S. warneri can cause IE in a patient with valvular heart disease without medical device. To our best of knowledge, there were only 12 case reports, including our case, on IE caused by S. warneri in the English language literature (Table 1)12–22. The cases had a mean age of 56 years (range, 32–79 years), and 3 of 12 cases were women. In Table 1, 7 of 12 patients (58.3%) without medical device developed IE. Of these patients, three were immunocompromised because of liver cirrhosis, renal cell carcinoma, and type 1 diabetes mellitus. Two of the three immunocompromised patients underwent skin incision, which could have been one of the risk factors for S. warneri IE. The present patient did not have any medical device or skin incision. Instead, mitral valve regurgitation was considered to have predisposed the patient to develop native valve endocarditis (NVE). Review of CoNS NVE cases showed an incidence of 34% among the cases that had valvular heart disease23. Elderly people have been pointed to be more likely to have degenerative valvular heart diseases24. Moreover, patients with valvular heart disease had been discussed to be at risk of developing NVE caused by CoNS, including S. warneri . Detection of S. warneri in the blood culture of patients with valvular heart disease of any kind should not be merely recognized as contamination, and physicians should pay attention to the development of IE.
Second, S. warneri IE can run a severe course, such as development of disseminated lesions, in patients without any comorbidity. As shown in Table 1, the mortality rate of S. warneri IE and NVIE was 8.3% (1 of 12 cases) and 11.1% (1 of 9 cases). In the systematic reviews on CoNS infections, including S. warneri NVE, the reported mortality rate was 19% to 25%23, 25, 26. The present patient had disseminated lesions, such as left cerebellar infarction, spondylitis, and discitis. Moreover, 4 of 12 cases (33.3%) shown in Table 1 had disseminated lesions. In the systematic reviews on CoNS NVE, the reported incidence rate of disseminated lesions was 22%26.
Although S. warneri , unlike most other CoNS, has not been recognized frequently as a significant human pathogen, the mortality rates were higher for S. warneri and CoNS than forStreptococcus viridans 26. The high CoNS NVE mortality has two possible reasons, including the delay in making a diagnosis and the background comorbidities of patients. CoNS, includingS. warneri , is slow-growing, may lead to an indolent course, and most commonly contaminate blood culture15, all of which can lead to delayed diagnosis. Chu et al. reported in a cohort study that patients who had CoNS NVE, compared with patients who hadS. viridans group NVE, were more likely to be older (median age, 68 years vs. 59 years) and had more prolonged indwelling intravascular catheter (20.0% vs. 1.0%) or healthcare-associated IE (40.0% vs. 1.34%)26. Table 1 shows that of 8 cases (median age, 62 years) that had S. warneri NVE, 2 (25%) had a medical device and 6 (75%) had comorbidities, such as liver cirrhosis, renal cell carcinoma, bilateral heart enlargement, disc prothesis, and degenerative aortic valve disease.
In conclusion, we reported a case of NVE caused by S. warneriassociated with spondylitis and cerebellar infarction in an elderly patient who had recognized mitral valve regurgitation for many years without heart valvular prosthesis. S. warneri can cause IE in a patient without medical device and can run a severe course, such as development of disseminated lesions. When blood cultures reveal S. warneri in patients with valvular heart diseases, physicians should consider IE. In the era of a severely aging population, physicians should pay attention to look for both IE and disseminated lesions when blood cultures reveal S. warneri, especially in elderly people with valvular heart disease.