STEFANO BASSETTI, SARAH WASMER, PAUL HASLER, THOMAS VOGT, DANICA NOGARTH, RENO FREI, and ANDREAS F. WIDMER

ABSTRACT.

Objective. To compare the prevalence of nasal and oral Staphylococcus aureus in patients with rheumatoid arthritis (RA) with the prevalence in controls with other rheumatic diseases, and to determine predictors of S. aureus carriage and the influence of treatment with anti-tumor necrosis factor-a (anti-TNF-a) agents.

Methods. Eighty-one patients with RA and 83 other control patients of 2 outpatient rheumatology clinics were cultured for nasal and oral carriage of S. aureus. Quantitative nasal cultures for S. aureus were performed from swabs of the anterior nares, the posterior pharynx, and the soft palate. Information on medications, medical conditions, and risk factors for S. aureus carriage was collected from all participants by a questionnaire and confirmed by chart review.

Results. The S. aureus carriage rate (nasal and/or oral colonization) was 34.6% among RA patients and 32.5% among controls (p = 0.87). Being treated with an anti-TNF-a agent plus methotrexate (MTX) was the only independent predictor of S. aureus carriage (OR 3.24, 95% CI 1.16–9.05, p = 0.025). The S. aureus carriage rate among RA patients treated with an anti-TNF-a agent plus MTX was 60% (9/15) versus 23.1% (3/13) in RA patients treated with an anti-TNF-a agent only (p = 0.049). All S. aureus isolates were susceptible to oxacillin.

Conclusion. The S. aureus carriage rate among patients with RA was not higher than among controls. Treatment with anti-TNF-a agents was not associated with an increased S. aureus carriage rate. However, treatment with an anti-TNF-a agent plus MTX may predispose patients to S. aureus carriage. (J Rheumatol 2005;32:2125-9)

Key Indexing Terms:

STAPHYLOCOCCUS AUREUS
RHEUMATOID ARTHRITIS
CARRIAGE
COLONIZATION
ANTI-TUMOR NECROSIS FACTOR-a THERAPY
TUMOR NECROSIS FACTOR-a

From the Division of Infectious Diseases and Hospital Epidemiology, Microbiology Laboratory, University Hospital Basel, Basel; University Department of Rheumatology, Felix Platter-Spital, Basel; and Department of Rheumatology, Kantonsspital Aarau, Aarau, Switzerland.

Dr. Bassetti was supported by grants from the University of Basel (Sonderprogramm zur Förderung des akademischen Nachwuchses) and from the Department of Internal Medicine (VFWAWF), University Hospital Basel, Basel, Switzerland.

S. Bassetti, MD, Assistant Professor of Medicine, University of Basel, Senior Registrar; S. Wasmer, Med Pract, Resident, Division of Infectious Diseases and Hospital Epidemiology, University Hospital Basel; P. Hasler, MD, Professor of Medicine, University of Basel, Head of Rheumatology, Kantonsspital Aarau; T. Vogt, MD, Staff Physician, University Department of Rheumatology, Felix Platter-Spital; D. Nogarth, Laboratory Technician, Division of Infectious Diseases and Hospital Epidemiology, and Microbiology Laboratory, University Hospital Basel; R. Frei, MD, Head of Microbiology, University Hospital Basel; A.F. Widmer, MD, MS, Professor of Medicine, University of Basel, Head of Hospital Epidemiology, University Hospital Basel.

Address reprint requests to Dr. S. Bassetti, Division of Infectious Diseases and Hospital Epidemiology, University Hospital Basel, CH-4031 Basel, Switzerland. E-mail: sbassetti@uhbs.ch

Accepted for publication June 3, 2005.

Patients with rheumatoid arthritis (RA) are at increased risk of developing infections and appear to be particularly susceptible to septic arthritis, osteomyelitis, and skin and soft tissue infections¹, which are mostly caused by Staphylococcus aureus. This bacterium is responsible for up to 80% of joint infections in patients with RA². The risk of severe infections may be even higher in RA patients treated with anti-tumor necrosis factor-a (TNF-a) agents³, which are increasingly used as monotherapy or in combination with methotrexate (MTX)⁴. It has been shown that S. aureus and other gram-positive bacteria are potent inducers of TNF-a secretion from macrophages⁵, that TNF-a enhances killing of S. aureus by neutrophils⁶, and that a local increase in TNF levels might improve host defenses against staphylococcal foreign body infections⁷. These observations suggest that inhibition of TNF-a affects the response of the body to colonization and infection with S. aureus. Indeed, in a recent study, nasal colonization with S. aureus was found in 5 of 8 (63%) RA patients treated with etanercept, but in only 10 of 39 (26%) RA patients treated without anti-TNF-a agents⁸.

Nasal S. aureus carriage appears to play a key role in the pathogenesis of infection^9,10. S. aureus nasal carriers have a 2- to 12-fold higher risk of S. aureus infection than noncarriers¹⁰. A large multicenter study demonstrated that 82% of patients with S. aureus bacteremia carried in their anterior nares the same S. aureus strain isolated from the blood, strongly suggesting that most cases of S. aureus bacteremia originate from S. aureus colonizing the nose¹¹. In another study, 14,008 nonbacteremic, nonsurgical patients were screened for nasal S. aureus at hospital admission and were monitored for the development of bacteremia. Nosocomial S. aureus bacteremia was 3 times more frequent in S. aureus carriers than in noncarriers¹². Moreover, the number of nasal S. aureus colony-forming units (CFU) influences the risk of subsequent infection in carriers. White obtained quantitative nasal cultures from patients before surgery and found that the incidence of postoperative S. aureus infections rose progressively in patients with progressively larger numbers of S. aureus in the nose¹³. Heavy nasal S. aureus carriers (> 100,000 CFU per swab) had a significantly higher infection rate compared with noncarriers. On the other hand, the elimination of nasal carriage (decolonization) can decrease the rate of nosocomial S. aureus infections among S. aureus carriers¹⁴. However, additional studies are necessary to identify patients who would benefit the most from prophylactic decolonization¹⁴.

In the general population, the nasal S. aureus carriage rate is about 30%⁹, but it is still unknown why an individual carries S. aureus. Three other studies reported the prevalence of S. aureus colonization among patients with RA and found a significantly higher S. aureus nasal carriage rate (50%–56% vs 28%–33%)^15,16 and oral carriage rate (14%–56% vs 4%–24%)^15,17 among patients with RA than among healthy controls.

Our objectives were to compare the prevalence of nasal and oral S. aureus carriage in outpatients with RA with the prevalence in outpatients with other rheumatic diseases (controls), and to investigate predictors of S. aureus carriage, in particular the influence of treatment with anti-TNF-a agents.

MATERIALS AND METHODS

Patients. The study population consisted of a volunteer sample of outpatients treated at the outpatient rheumatology clinics of the University Department of Rheumatology, Felix Platter-Spital, Basel, and of the Kantonsspital Aarau, Aarau, Switzerland. Both centers provide primary and tertiary care. Consecutive patients attending clinics were asked to participate. There were no exclusion criteria. All subjects with RA were diagnosed by a rheumatologist and met classification criteria for RA established by the American College of Rheumatology¹⁸. At least one of 2 rheumatologists (PH and TV) either diagnosed RA or confirmed the diagnosis in all patients. Subjects in the control group were patients treated at or referred to the same 2 rheumatology clinics for any disorder other than RA.

Written informed consent according to the Declaration of Helsinki was obtained from each study participant. The study was approved by the Research Ethics Committee of the Cantons Basel-Stadt and Basel-Land, and by the Ethics Committee of the Kantonsspital Aarau.

Risk factors for S. aureus carriage. All participants were interviewed. Information on medications, medical conditions, and risk factors for S. aureus carriage^9,19,20 was collected by a structured questionnaire and verified by chart review. The presence or absence of the following risk factors or postulated risk factors for S. aureus was systematically recorded: renal insufficiency requiring dialysis, human immunodeficiency virus (HIV) infection, atopic dermatitis, insulin-dependent diabetes mellitus, intravenous drug abuse, and all factors listed in Tables 1 and 2.

Microbiological studies. Specimens were obtained with a sterile polyester fiber-tipped swab moistened with sterile saline from the anterior nares (5 rotations in each anterior nostril), the posterior wall of the pharynx, and the soft palate. Swabs were taken to the laboratory in a transport tube (Transwab^® MW170; Medical Wire & Equipment Co., Corsham, UK) and processed within 24 h. Each swab was placed in a tube with phosphate buffered saline (PBS; at the beginning of the study 4 ml, later 2 ml), sonicated for 1 min (35 kHz), and vortexed for 15 s. The PBS was then serially diluted and surface-plated on Columbia sheep blood agar¹⁹. After incubation at 35°C for 24 h and at room temperature for a further 24 h, colonies with morphology consistent with S. aureus were counted and identified by Gram stain, catalase test, and latex agglutination test for the detection of clumping factor, protein A, and capsular polysaccharides of S. aureus (Pastorex^® Staph-Plus; Bio-Rad, Marnes-la-Coquette, France). Susceptibility testing for oxacillin was performed with oxacillin screening agar plates (6 mg/l) according to National Committee for Clinical Laboratory Standards guidelines²¹.

Statistical analysis. Categorical variables were compared using a 2-sided chi-square test or Fisher's exact test, and continuous variables using the t test. S. aureus CFU counts among carriers were logarithmically transformed before analysis with parametric tests. Independent predictors of S. aureus carriage were determined by multiple stepwise logistic regression analysis. All variables with p value ≤ 0.10 were entered into the model. Statistical analyses were performed using SPSS (v. 10.1.3; SPSS, Chicago, IL, USA).

RESULTS

Table 1. Characteristics of patients with RA and controls (patients without RA).

Table 2. Characteristics of S. aureus carriers (colonization of nose, pharynx, or palate) and noncarriers.

Study population. Eighty-one patients with RA and 83 patients without RA (controls) were studied. The demographic characteristics of participants and characteristics that could affect the S. aureus carriage rate are presented in Table 1. Among the patients with RA, the mean duration of disease was 12 years (SD 9 yrs). No patient had atopic dermatitis, HIV infection, or renal insufficiency requiring dialysis. No intravenous drug user was included. Two patients had insulin-dependent diabetes mellitus; neither was colonized with S. aureus.

S. aureus carriage. The S. aureus colonization rate of nose, posterior pharynx, and soft palate was similar in RA patients and in controls (Table 1). Overall, 28/81 (34.6%) RA patients and 27/83 (32.5%) controls were S. aureus carriers. S. aureus was cultured more frequently from the anterior nares than from the oropharynx. The S. aureus carriage rate among RA patients treated with an anti-TNF-a agent plus MTX was 60% (9/15) versus 23.1% (3/13) in RA patients treated with an anti-TNF-a agent only (p = 0.049).

Risk factors for S. aureus carriage. Characteristics associated with S. aureus carriage are presented in Table 2. The following variables were included in the logistic regression analysis model: age, allergic rhinitis, psoriasis, and combination treatment with an anti-TNF-a agent plus MTX. In this model, the only independent predictor of S. aureus carriage was being treated with an anti-TNF-a agent plus MTX (OR 3.24, 95% CI 1.16–9.05, p = 0.025).

Quantitative S. aureus cultures. The highest counts of S. aureus CFU were found in the nose. Carriers with RA had similar S. aureus counts as carriers without RA. Treatment with an anti-TNF-a agent or with an anti-TNF-a agent plus MTX did not appear to affect S. aureus counts (Figure 1).

[click, then close, image]

Figure 1. Results of quantitative cultures. Mean log10 ± SD of CFU of S. aureus in the nose and posterior pharynx and on the soft palate in S. aureus carriers with or without rheumatoid arthritis (A); in S. aureus carriers with or without anti-TNF-a therapy (B); and in S. aureus carriers with or without therapy with an anti-TNF-a agent and methotrexate (C).

Susceptibility to oxacillin. All S. aureus isolates were susceptible to oxacillin.

DISCUSSION

The S. aureus colonization rate among patients with RA (34.6%) was similar to the colonization rate in patients without RA (32.5%), and also to the mean carriage rate of 37.2% calculated by Kluytmans, et al for the general population from 18 published studies involving 13,873 individuals⁹. This indicates that RA does not increase the risk for S. aureus colonization. The only independent predictor of S. aureus carriage was being treated with an anti-TNF-a agent plus methotrexate.

Three other studies have reported S. aureus carriage rates among RA patients. In the study by Jacobson, et al¹⁷ cultures were obtained from the posterior wall of the pharynx, saliva, tongue, and gingival crevices. Patients with RA had a significantly higher prevalence of oral S. aureus than controls (14% vs 4%). Of 16 RA patients with S. aureus identified in at least one of the oral sites, 13 (81%) had S. aureus cultured from their posterior pharynx, suggesting that the posterior oropharynx may be the source of oral S. aureus, and that colonization of the mucosal surfaces proceeds from the nares (the main reservoir of S. aureus) into the oropharynx, and from there to the oral cavity. Jackson, et al¹⁵ found that a significantly higher proportion of RA patients were nasally (56%) or orally (56%) colonized with S. aureus in comparison to healthy adults (28% and 24%, respectively). Finally, Tabarya and Hoffman¹⁶ found a S. aureus nasal carriage rate of 50% among RA patients and 33% among healthy controls.

The increased S. aureus carriage rate among RA patients reported in these 3 studies contrasts with our findings. However, important differences in RA patients and/or control subjects included in these studies may explain the different results. In particular, Jacobson, et al¹⁷ included only RA patients with longterm (> 6 months) corticosteroid therapy, and Jackson, et al¹⁵ only patients "receiving treatment for RA" (treatment was not reported). Moreover, all 3 studies compared RA patients with healthy controls and did not consider other well known risk factors for S. aureus carriage^9,19,20 that may have affected colonization rates significantly, such as previous hospitalization, or the presence of psoriasis or allergic rhinitis. Further, quantitative cultures were not performed.

The main limitation of our study is the relatively small number of patients included. In addition, RA patients treated at outpatient rheumatology clinics may be not representative of all patients with RA.

We found that in colonized patients S. aureus was cultured more frequently from the nose than from the oropharynx. These findings are in agreement with a recent study reporting a nasal colonization rate of 25.6% among RA patients⁸, and with many studies showing that the anterior nares are the ecological niches of S. aureus and the most consistent area from which this organism can be isolated⁹.

In our study, the only independent predictor of S. aureus carriage was being treated with an anti-TNF-a agent plus MTX, suggesting that this combination therapy may predispose to S. aureus carriage and therefore increase the risk of S. aureus infections. The reasons for this association are unclear. One may speculate that the combined effects of an anti-TNF-a agent and MTX²² on cytokine production may influence the adhesion of S. aureus to nasal epithelial cells and mucosae. On the other hand, the combination therapy consisting of an anti-TNF-a agent plus MTX may have been used in more severe cases of RA. These patients may have particular characteristics, for example, of nasal epithelial cells or of nasal mucin, that are not present in other RA patients and which may favor adhesion of S. aureus.

Quantitative cultures in our study showed higher S. aureus counts in the nose than in the oropharynx, confirming the predilection of S. aureus for the anterior nares. However, the variability of S. aureus counts was high, and larger studies are necessary to conclusively address the factors influencing S. aureus counts in carriers.

All S. aureus isolates in this study were susceptible to oxacillin. This is not surprising, considering the relatively low prevalence of methicillin-resistant S. aureus in northwestern Switzerland²³, even among risk groups such as intravenous drug users²⁰.

The carriage rate of S. aureus among patients with RA was not higher than among controls with other rheumatic diseases. However, patients treated with an anti-TNF-a agent plus methotrexate had high colonization rates of S. aureus and might have a higher risk of S. aureus infections.

ACKNOWLEDGMENT

We thank Margot von Dechend, MD, Department of Rheumatology, Kantonsspital Aarau, for help in the recruitment of patients.

REFERENCES

Search PubMed for:

2. Goldenberg DL. Septic arthritis. Lancet 1998;351:197-202. [MEDLINE]

3. Kroesen S, Widmer AF, Tyndall A, Hasler P. Serious bacterial infections in patients with rheumatoid arthritis under anti-TNF-alpha therapy. Rheumatology Oxford 2003;42:617-21. [MEDLINE]

4. Klareskog L, van der Heijde D, de Jager JP, et al. Therapeutic effect of the combination of etanercept and methotrexate compared with each treatment alone in patients with rheumatoid arthritis: double-blind randomised controlled trial. Lancet 2004;363:675-81. [MEDLINE]

5. Keller R, Fischer W, Keist R, Bassetti S. Macrophage response to bacteria: induction of marked secretory and cellular activities by lipoteichoic acids. Infect Immun 1992;60:3664-72. [MEDLINE]

6. Ferrante A, Martin AJ, Bates EJ, et al. Killing of Staphylococcus aureus by tumor necrosis factor-alpha-activated neutrophils. The role of serum opsonins, integrin receptors, respiratory burst, and degranulation. J Immunol 1993;151:4821-8. [MEDLINE]

7. Vaudaux P, Grau GE, Huggler E, et al. Contribution of tumor necrosis factor to host defense against staphylococci in a guinea pig model of foreign body infections. J Infect Dis 1992;166:58-64. [MEDLINE]

8. Ferraccioli G, Mecchia F, Di Poi E, Fabris M. Anticardiolipin antibodies in rheumatoid patients treated with etanercept or conventional combination therapy: direct and indirect evidence for a possible association with infections. Ann Rheum Dis 2002;61:358-61. [MEDLINE]

9. Kluytmans J, van Belkum A, Verbrugh H. Nasal carriage of Staphylococcus aureus: epidemiology, underlying mechanisms, and associated risks. Clin Microbiol Rev 1997;10:505-20. [MEDLINE]

10. Perl TM, Golub JE. New approaches to reduce Staphylococcus aureus nosocomial infection rates: treating S. aureus nasal carriage. Ann Pharmacother 1998;32:S7-16. [MEDLINE]

11. von Eiff C, Becker K, Machka K, Stammer H, Peters G. Nasal carriage as a source of Staphylococcus aureus bacteremia. N Engl J Med 2001;344:11-6. [MEDLINE]

12. Wertheim HF, Vos MC, Ott A, et al. Risk and outcome of nosocomial Staphylococcus aureus bacteraemia in nasal carriers versus non-carriers. Lancet 2004;364:703-5. [MEDLINE]

13. White A. Increased infection rates in heavy nasal carriers of coagulase-positive staphylococci. Antimicrob Agents Chemother 1963;161:667-70.

14. Perl TM, Cullen JJ, Wenzel RP, et al. Intranasal mupirocin to prevent postoperative Staphylococcus aureus infections. N Engl J Med 2002;346:1871-7. [MEDLINE]

15. Jackson MS, Bagg J, Gupta MN, Sturrock RD. Oral carriage of staphylococci in patients with rheumatoid arthritis. Rheumatology Oxford 1999;38:572-5. [MEDLINE]

16. Tabarya D, Hoffman WL. Staphylococcus aureus nasal carriage in rheumatoid arthritis: antibody response to toxic shock syndrome toxin-1. Ann Rheum Dis 1996;55:823-8. [MEDLINE]

17. Jacobson JJ, Patel B, Asher G, Woolliscroft JO, Schaberg D. Oral staphylococcus in older subjects with rheumatoid arthritis. J Am Geriatr Soc 1997;45:590-3. [MEDLINE]

18. Arnett FC, Edworthy SM, Bloch DA, et al. The American Rheumatism Association 1987 revised criteria for the classification of rheumatoid arthritis. Arthritis Rheum 1988;31:315-24. [MEDLINE]

19. Bassetti S, Dunagan DP, D'Agostino RB Jr, Sherertz RJ. Nasal carriage of Staphylococcus aureus among patients receiving allergen-injection immunotherapy: associated factors and quantitative nasal cultures. Infect Control Hosp Epidemiol 2001;22:741-5. [MEDLINE]

20. Bassetti S, Wolfisberg L, Jaussi B, et al. Carriage of Staphylococcus aureus among injection drug users: lower prevalence in an injection heroin maintenance program than in an oral methadone program. Infect Control Hosp Epidemiol 2004;25:133-7. [MEDLINE]

21. National Committee for Clinical Laboratory Standards. Performance standards for antimicrobial susceptibility testing: Eleventh informational supplement. Wayne, PA: National Committee for Clinical Laboratory Standards; 2001: Document M100-S11.

22. Gerards AH, de Lathouder S, de Groot ER, Dijkmans BA, Aarden LA. Inhibition of cytokine production by methotrexate. Studies in healthy volunteers and patients with rheumatoid arthritis. Rheumatology Oxford 2003;42:1189-96. [MEDLINE]

23. Blanc DS, Pittet D, Ruef C, et al. Epidemiology of methicillin-resistant Staphylococcus aureus: results of a nation-wide survey in Switzerland. Swiss Med Wkly 2002;132:223-9. MEDLINE]