Infective endocarditis caused by Gram-negative bacilli is rare and commonly considered to be primarily a disease of IVDUs2 Staphylococcus aureus
is the organism most frequently isolated (60% to 90%)3
in cases of TVE as it naturally colonises the skin and is commonly introduced by IVDUs. Other causative organisms of TVE include Candida species, especially Candida glabrata
, Streptococcus bovis
, Gemella morbillorum
and Pseudomonas aeruginosa
Most bacteria can of course cause native valve endocarditis (NVE), however it is rare to contract E coli
NVE, with only 36 cases being reported between 1902 and 2002.3
Micol et al5
reported that the majority of cases were in older (>70 years) women, with the urinary tract being the most common portal of entry. Of the 36 cases reviewed, 20 involved the mitral valve with no specific number documented for tricuspid valve involvement. A literature search found only one case report, by Magalhaes et al
of TVE due to E coli
in a 16-year-old boy with no predisposing risk factors for endocarditis.
As reported by Jauréguy et al
bacteraemia from E coli
is one of the most common bloodstream isolates, for which it is associated with a high rate of morbidity and mortality. Although the extraintestinal pathogenic E coli
strains are rarely responsible for endocarditis, clinicians will frequently encounter E coli
bacteraemia with some reports suggesting that it accounts for approximately 20% of all clinically significant bloodstream isolates. Therefore the differential diagnosis of endocarditis is important and should never be discounted when faced with E coli
This case was not atypical of infective endocarditis, with the patient having subacute pyrexia of unknown origin. The patient's history and clinical presentation fulfilled both major criteria of the modified Duke's criteria.8
There were two separate occasions in which blood cultures grew E coli
. Unfortunately, despite extensive investigations and reviewing the chronology of the patient's history the portal of entry of the micro-organism was never found. We can only propose that we were unlucky in missing the portal of entry or that the true causative organism was never cultured. It was disappointing but not unexpected that cultures of the valve scrapings were negative due to the long course of intravenous antibiotics that the patient had received prior to surgery. This case highlights that TVE is rarely considered in the differential diagnosis of a patient who is febrile who does not use intravenous drugs, however it is an important differential diagnosis that must never be forgotten, especially as this is not an exceptional case but rather emphasises, as reported by Heydari et al
that isolated TVE continues to occur, eluding diagnosis and sometimes only discovered at autopsy.
Throughout this patient's admission expert microbiological advice was sought. Her antibiotic treatment was felt sufficient to cover E coli as well as other Gram-negative bacilli. It was unusual to see only a partial response after 6 weeks of a therapeutic regime.
The ESC guidelines3
recommend that surgical treatment should be considered, as follows, in cases of treatment resistant right-sided infective endocarditis.
- Micro-organisms difficult to eradicate or bacteraemia >7 days despite adequate antimicrobial treatment, or
- Persistent tricuspid valve vegetation (>20 mm) after recurrent pulmonary emboli with or without concomitant right heart failure.
The guidelines advocate valvectomy without prosthetic replacement, which is what our patient underwent.
Although the ESC guidelines provide specific parameters this report highlights a common problem faced by clinicians, as was found in this case, in terms of optimal timing for tricuspid valve surgery. There appears to be no universal agreement. A study by Sung et al9
found that earlier operative timings may improve early outcomes, however these favourable results could not be satisfactorily explained. The general consensus is that it would be unwise to delay surgery because of the potentially high operative mortality.
Sung et al9
suggest that tricuspid tissue valve repair can nowadays be performed with low operative mortality achieved through optimal perioperative management. A study by Bleiweis et al10
was unable to isolate any significant pre/intraoperative risk factors for operative death, however both studies9 10
recognise that certain strategies, such as improved myocardial protection, optimal perioperative care and modified ultrafiltration, play an important role in lowering operative mortalities.
In conclusion, our patient was fortunate to have made such a successful full recovery from TVE and surgery. The case presented with atypical bacteria, she had no evidence of intravenous drug use, she was not infected with HIV or hepatitis and she herself vehemently denied any intravenous drug use. We have no reason to suspect otherwise, and for that very reason we were lost without Occam's razor.
- There should always be a high index of suspicion for infective endocarditis in patients who present with a clinical picture of persistent fever (>38 °C) of unknown origin, even in young, normal subjects.
- Clinicians should be aware that the prevalence of tricuspid valve endocarditis (TVE) in non-intravenous drug users (non-IVDUs) is rising.1
- In accordance with the European Society of Cardiology (ESC) guidelines there is no rationale for delaying blood culture sampling to coincide with peaks of fever.3