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Introduction
Weeksella virosa (W. virosa) is one of the two species of the genus Weeksella and belongs to the family Flavobacterium; it was named in honor of O.B. Weeks for his contributions to the taxonomy1. Strains of W. virosa have been detected in the genitourinary tract, oral cavity, rectal area, middle ear, mastoid, and cerebrospinal fluid by culture methods2. Holmes et al. found 72.3% of the strains in urine samples or genitourinary tract3. Clinical disease in humans is rare; only nine cases have been reported. The most common clinical syndrome is characterized by spontaneous bacterial peritonitis, although sepsis, pneumonia, ventriculitis, and urinary tract infection have been described. Among the nine cases reported, only the one reported by Manoragan et al. describes W. virosa as a cause of death in a 53-year-old patient with lymphoma4.
In the present study, the first clinical report of bacteremia due to W. virosa in an immunocompromised pediatric patient is described.
Clinical case
A 4-year-old male patient diagnosed as a Stage III left orbit rhabdomyosarcoma in 2016 with left orbital enucleation in 2018 and multiple hospitalizations due to neutropenic fever was admitted to Hospital Universitario Dr. José Eleuterio González in June 2019. The patient received a last dose of chemotherapy with ifosfamide, mesna, carboplatin, and etoposide 10 days before admission.
The patient started with a fever (38.6°C), cough, and odynophagia, accompanied by diarrheic evacuations. A physical examination showed a 38°C fever and a 100/min heart rate. Pharyngeal erythema was detected, as well as hypertrophic tonsils and hyperemic left tympanic membrane with hyaline rhinorrhea. According to the protocol for fever and neutropenia in children, imipenem/cilastatin was initiated within the first hour of admission, and a sample for blood culture was collected. The laboratory tests revealed severe neutropenia (200 cells/mm3) and C-reactive protein values of 24 mg/dl.
The patient showed a favorable clinical course with remission of the respiratory symptoms and fever on days 2 and 3 of hospital stay, respectively. The remission of neutropenia was documented after four days. Lab test results were as follows: hemoglobin, 9.93 g/dl; white blood cell count (WBC), 1.56 cells/mm3; neutrophils (Neu), 0.756 cells/mm3; and platelets, 43.6 cells/mm3. Blood culture was processed in a VersaTREK REDOX 1 aerobic EZ Draw 40 ml bottle (ThermoFisher, Scientific). Gram staining of blood culture broth revealed Gram-negative rods. Meropenem was initiated due to its better activity against Pseudomonas aeruginosa and Acinetobacter baumannii, which are agents of high prevalence in this institution. The broth was plated on blood, chocolate, and MacConkey agar and incubated in aerobiosis. Subsequent examination of the plates revealed abundant growth of colonies on blood agar. The growth in MacConkey agar was found negative. The identification was performed by Sensititre ARIS 2X ID/AST System-Thermo Fisher Scientific, which reported W. virosa. The pathogen was susceptible to amikacin, gentamicin, ampicillin, cefuroxime, ciprofloxacin, piperacillin/tazobactam, and tetracyclines.
After 10 days of treatment with intravenous meropenem, outpatient management was indicated with ciprofloxacin for 14 days, with favorable results.
Discussion
Weeksella species named Flavobacterium genitale initially due to its preponderance for the urogenital tract are oxidase-positive and catalase-positive Gram-negative rod, which are unable to grow on MacConkey agar1. The organism will grow on blood and chocolate agar after 48 h of incubation at 22°C, 36°C, and 42°C. Culture will reveal 2 mm of diameter cream-colored and intensely mucous colonies, with an appearance of yellow tinge secondary to a non-diffusible pigment2,5.
Two species of Weeksella have been identified: W. virosa and Weeksella zoohelcum2. The latter species have been isolated from human wounds caused by animal bites.
The overall incidence of this bacterium documented by Holmes et al.3 in the urogenital tract was 2% of the female population, with a higher incidence in a group exposed to sexually transmitted diseases6. More recent reports have shown a varying incidence from 0.42 to 15%6.
Since 1970, clinical cases of W. virosa have rarely been isolated. In a literature search between 1990 and 2019, nine cases with W. virosa infection were found (Table 1). A review of these cases revealed the following clinical syndromes: spontaneous bacterial peritonitis (2/9), sepsis (2/9), urinary tract infection (2/9), pneumonia (1/9), and surgical head wound infection with ventriculitis (1/9), amnionitis (1/9), and wound infection (1/9). Six of the ten cases, including the current case, were found during the past decade, probably indicating an increased incidence of this organism in humans. At present, no risk factors have been implied, but all of the patients showed at least one comorbidity, including diabetes mellitus (2/9), end-stage renal disease (3/9), hepatitis C virus infection (1/9), ischemic heart disease (1/10), lymphoma (1/9), or anaplastic meningioma (1/9). Of the ten cases, this organism was isolated from two blood cultures in patients with lymphoma and hepatitis C virus infection, respectively. Tatum et al. documented two of 76 blood Group I organism isolates in the Centers for Disease Control and Prevention between 1947 and 1973. However, the clinical features in these cases were not documented, although success was reported in five of nine patients7. In comparison to the current case, a correlation between the site of infection and the symptoms presented is described. In one case, a fatal outcome occurred with the involvement of W. virosa in pneumonia8.
Table 1 Weeksella virosa case series
| Author | Year | Age | Sex | Comorbidities | Source | Clinicalsyndrome | Treatment | Outcome |
|---|---|---|---|---|---|---|---|---|
| Faber et al.11 | 1991 | 33 | F | ESRF on PD | Peritoneal fluid | SBP | Imipenem, cilastatin | Survived |
| Boixeda et al.12 | 1998 | 55 | M | HCV, cirrhosis | Peritoneal fluid | SBP | Cefoxitin | Survived |
| Meharwal et al.13 | 2002 | NR | NR | NR | Urine | UTI | NR | NR |
| Manoragan et al.4 | 2004 | 53 | F | Lymphoma, DM, ESRF on HD | Blood, sputum | Pneumonia | Cefepime, vancomycin | Died |
| Slenker et al.8 | 2012 | 44 | F | Obesity, menorrhagia | Wound | Sepsis | Incision and drainage | Survived |
| 31 | F | IHD, ESRF, HCV, obesity, asthma | Blood | Labial woundinfection | Aztreonam, tobramycin | Died | ||
| 25 | F | Spontaneous vaginal delivery | Placenta | Amnionitis | Ampicillin, gentamicin | Survived | ||
| 26 | F | Endometriosis, abdominopelvicadhesiolysis, DM | Urine | UTI | Trimethoprim-sulfamethoxazole | Survived | ||
| Toescu et al.14 | 2017 | 50 | F | Anaplasticmeningioma, glucocorticoid use, WBRT | Cranialwound, brainventricle | Craniotomywoundinfection, ventriculitis | Ceftriaxone, amoxicillin | Survived |
| Currentreport | 2019 | 4 | M | Embryonalrhabdomyosarcoma | Blood | Bacteremia | Imipenem, meropenem | Survived |
F: female; M: male; ESRF: end-stage renal failure; PD: peritoneal dialysis; SBP: spontaneous bacterial peritonitis; HCV: hepatitis C virus; NR: not reported; UTI: urinary tract infection; DM: diabetes mellitus; HD: hemodialysis; IHD: ischemic heart disease; WBRT: whole-brain radiotherapy.
Modified from Slenker et al.6
No species-specific testing standards exist for this organism; however, the Clinical and Laboratory Standards Institute susceptibility testing interpretative standard table for other non-Enterobacteriaceae Gram-negative rods can be used9. Resistance has been noted in vitro with aminoglycosides, nalidixic acid, and nitrofurantoin10,11. According to previous reports, our institutional protocol represents a viable coverage for W. virosa. Until the present day, only two deaths associated with W. virosa have been reported: in one case, the initial empirical treatment was not effective for W. virosa, and the second case was a patient with multiple comorbidities.
The present report describes a patient with bacteremia, who presented a neutropenic fever episode. The initial choice of antimicrobial treatment was imipenem/cilastatin, according to the Infectious Diseases Society of America (IDSA) guidelines for the use of antimicrobial agents in neutropenic patients with cancer. For fever and neutropenia, IDSA guidelines suggest the empirical treatment with cefepime, piperacillin/tazobactam, or imipenem/cilastatin. However, the identification of new pathogens with recent technology would be an opportunity to review the standard treatment. The patient survived the episode and was discharged fully recovered from the hospital. To the best of our knowledge, this is the first case of W. virosa bacteremia documented in Mexico, and the first pediatric case reported. Furthermore, not only adults but also children with comorbidities, such as renal disease, liver disease, or oncology disease, should be considered a high-risk population for W. virosa infection.
In conclusion, this is the first case of W. virosa bacteremia in a pediatric patient with embryonal rhabdomyosarcoma. The identification of new pathogens by molecular techniques should be an opportunity to reassess the empirical therapies established so far.
