Meningitis due to an unusual human pathogen: Streptococcus equi subspecies equi.

Abstract: Streptococcus equi subspecies equi is involved in human infection. We present a case of meningitis in a 75-year-old patient with a favorable outcome after ceftriaxone and dexamethasone therapy. To our knowledge, it is the first case reported in an adult.

Key Words: Streptococcus equi subspecies equi, bacterial meningitis, meningitis in the elderly

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C group Streptococci are pathogenic for horses; in humans, these infections are uncommon and usually result in pharyngitis, skin and soft tissue infections, pneumonia, toxic shock-like syndrome, and endocarditis. When infection is associated with bacteremia, the reported mortality is high, at 25%. (1) Infection and especially invasive infection due to S. equi subspecies equi are very rare in humans; to our knowledge, only one case of S. equi subspecies equi meningitis has been reported, in a Canadian young boy. (2) We present a second case of meningitis due to S. equi subspecies equi in a 75-year-old woman, probably with an equine source. She was successfully treated with ceftriaxone and corticoids.

Case Report

A 75-year-old woman was admitted in April 2004 with fever, headache and stupor. She had a medical history of dilated cardiomyopathy with atrial fibrillation and heart failure in New York Heart Association stage III.

Three days before admission, she developed fever and headache; two days later she became confused and was referred to the infectious diseases department. She did not receive any antibiotics before admission. The physical examination at admission revealed a fever of 38.5[degrees]C. stupor, nuchal rigidity and Kernig sign. Laboratory tests showed inflammation (C-reactive protein, 126 mg/L), high WBCs, 20.9 X [10.sup.9]/L and renal failure with a creatinine level of 243 mmol/L. Computed tomography of the brain was negative for brain abscesses or tumors. Two blood cultures and a cerebrospinal fluid (CSF) culture was obtained in the first hour after admission. CSF analysis revealed a WBC count of 5.2 X [10.sup.9]/L (82% neutrophils and 18% lymphocytes), a protein concentration of 4.68 g/L and a glucose concentration of 0.62 mmol/L (peripheral blood glucose level at the same time being 7.3 mmol/L). No microorganisms were revealed on Gram stain of the CSF and latex agglutination was negative for N. meningitidis, S. pneumoniae and H. influenzae.

Initial treatment included ceftriaxone (4 g daily) and IV dexamethasone (8 mg four times daily). After 24 hours, the patient became apyretic and she came out of the stupor. On the third day of hospitalization, both blood cultures and CSF culture yielded group C Streptococcus, later identified with ID 32 STREP test as S. equi subspecies equi. The strain was susceptible to penicillin, ceftriaxone, clindamycin and levofloxacin and resistant to tetracycline. The patient stated that two neighbors are horse owners and she had visited their farm within the past two weeks. No attempt was made to recover S. equi subspecies equi from the horses on those farms and no horse illnesses were recorded.

The patient continued the treatment with ceftriaxone. She remained afebrile, and after 7 days of treatment, her headache disappeared and the renal failure was corrected. Ceftriaxone and dexamethasone were stopped on day 10, when the C-reactive protein reached a level of 4.12 mg/L and CSF analysis was almost normal. WBC count was 0.008 X [10.sup.9]/L, protein concentration was 0.57 g/L, and glucose concentration was 3 mmol/L (peripheral blood glucose level at the same time was 6.23 mmol/L). The patient was discharged home. At her 30-day follow-up visit, no relapse or sequelae had appeared, Unfortunately, two months later, the patient died with a severe ventricular arrhythmia.

Discussion

S. equi subspecies equi is a [beta]-hemolytic group C Streptococcus that causes strangles in horses. Since 1980, only four cases of S. equi subspecies equi were reported as an invasive infection in humans. (1-3) In these cases, direct contact with horses could be traced. For some human infections with a related species of Streptococcus equi subspecies zooepidemicus, ingestion of unpasteurized cow milk or contact with fresh horse manure was involved. (4-5)

The S. equi subspecies equi is a capsulated, ovoid or spherical bacteria from 0.6 to 1 [micro]m, assembled in short or long chains; colonies are mucous on blood agar. The S. equi subspecies equi identification with the automated system API ID 32 Strep was validated in 1992; in one study the overall rate of Streptococcus species identification was 95.3% (6) and Streptococcus equi subspecies equi ATCC 33 398 is one among the three strains used for quality control of API ID 32 Strep system. The antimicrobial susceptibility for the isolated strain was in concordance with previous peer-reviewed reports of infections in human and animals: sensitive to penicillin G, chloramphenicol, tetracycline and erythromycin. (7) In our patient, the ceftriaxone treatment was successful; indeed, in other case reports of invasive infection with S. equi, outcome was favorable with [beta]-lactam (penicillin or ceftriaxone) monotherapy. (1,8) These data could indicate that combined therapy [beta]-lactam and vancomycin is not mandatory, as stated by some authors. (9)

Meningitis is one of the localizations of invasive S. equi infections, and outcome could be severe, with high mortality. (1) The fatal outcome was reported also in other invasive infections with S. equi, often associated with a factor risk of extreme age: children or advanced age. (2,5,9-11) This condition, especially in the elderly, could be a confounding factor for an unfavorable outcome. In our case, the death occurred unrelated to the infection, two months after the meningitis episode, due to severe cardiac pathology.

Conclusion

S. equi subspecies equi infection is possible in humans, and may cause meningitis. The elderly could be a group at risk for severe infections with S. equi, but it is impossible to make this assessment, as to our knowledge, this is the first reported case.

References

1. Bradley SF, Gordon JJ, Baumgartner DD, et al. Group C streptococcal bacteremia: analysis of 88 cases. Rev Infect Dis 1991;13:270-280.

2. Elsayed S, Hammerberg O, Massey V, et al. Streptococcus equi subspecies equi (Lancefield group C) meningitis in a child. Clin Microbiol Infect 2003;9:869-872.

3. Breiman RF, Silverblatt FJ. Systemic Streptococcus equi infection in a horse handler--a case of human strangles. West J Med, 1986;145:385-386.

4. Francis AJ, Nimmo GR, Efstatiou A, et al. Investigation of milk-borne Streptococcus zooepidemicus infection associated with glomerulonephritis in Australia. J Infect 1993;27:1776-1780.

5. Lee AS, Dyer JR. Severe Streptococcus zooepidemicus infection in a gardener. MJA 2004;180:366.

6. Freney J, Bland S, Etienne J, et al. Description and evaluation of the semiautomated 4-hour rapid ID 32 Strep method for identification of streptococci and related genera. J Clin Microbiol 1992;30:2657-2661.

7. Gonzalez-Lama Z, Gonzalez JJ, Tejedor MT, et al. Sensitivity of groups A, B and C beta hemolytic streptococci to antibiotics. Rev Esp Quimioter 1999;12:215-219.

8. Downar J, Willey BM, Sutherland JW, et al. Streptococcal meningitis resulting from contact with an infected horse. J Clin Microbiol 2001; 39:2358-2359.

9. Shah SS, Matthews RP, Cohen C. Group C streptococcal meningitis: case report and review of the literature. Pediatr Infect Dis J 2001;20:445-448.

10. Ural O, Tuncer I, Dikici N, et al. Streptococcus zooepidemicus meningitis and bacteremia. Scand J Infect Dis 2003;35:206-207.

11. Bhally H, Casey K. Endogenous endophthalmitis secondary to Streptococcus group C infection. Infect Med 2004;21:128-130.

Gabriel-Adrian Popescu, MD, PHD, Raluca Fuerea, MD, and Elisabeta Benea, MD, PHD

From the Infectious Diseases Department, Matei Bals Infectious Diseases Institute, Bucharest, Romania.

Reprint requests to Gabriel-Adrian Popescu, MD, PhD, Matei Bals Infectious Diseases Institute, Grozovici, str, nr. 1, Sector 2, Bucharest, Romania

Accepted October 7, 2005.

RELATED ARTICLE: Key Points

* Streptococcus equi subspecies equi human transmission is possible even in a patient with minimal equine contact.

* Streptococcus equi is involved in severe human infections, such as meningitis.

* Ceftriaxone and corticosteroid treatment is successful.