Septic arthritis is a joint disease that can affect one or more joints in patients of any age.1 It is considered a medical emergency2 and, despite the new diagnostic techniques, the morbidity has changed little over the last 25 years.3 In Europe, the incidence is estimated to range between 2 and 6 cases per 100000 population4; this number can be multiplied by 10 among individuals with osteoarthritis or rheumatoid arthritis,5 those with a joint replacement, older persons, alcoholics, diabetics, immunocompromised patients, individuals with skin ulcers, those treated with intraarticular corticosteroids or synthetic materials6 and in indigenous populations.7

The organisms that cause septic arthritis differ from one part of the world to another.8 In the majority of the countries of Europe and North America, a greater frequency of staphylococci and streptococci has been reported.9 Gram-negative bacteria may be associated with septic arthritis in up to 20% of the cases, mainly when immunosuppression, cancer, diabetes or cirrhosis is involved.10 The diagnosis of septic arthritis is suspected on the basis of the clinical picture (joint pain, functional limitation and body temperature >38.5°C) and is confirmed by means of the gold standard, that is, a positive joint fluid culture.

In Mexico and the rest of Latin America, few studies have focused on septic arthritis from the perspective of comparing the major known risk factors to enable the application of this knowledge to similar geographic regions. Table 1 compares the microorganisms and clinical factors that have been associated with them in some of these studies. For the purpose of describing the medical history, clinical characteristics and microorganisms involved in a group of adults with and without a diagnosis of septic arthritis, we carried out a prospective comparative study in a tertiary care center in Mexico.

For the purpose of describing the clinical characteristics, microorganisms involved and comorbidities in a group of adults with septic arthritis, we reviewed the cases of acute arthritis in a tertiary care center in northeastern Mexico. A total of 96 patients in whom septic arthritis was suspected were studied. Ultimately, 49 cases were confirmed and were included as cases that were positive for septic arthritis, and the remainder, as a comparison group.

At the present time, it is increasingly common to find cases of polyarticular septic arthritis associated with rheumatoid arthritis, chronic diseases, antimicrobial resistance, aging or immunosuppression.3,11 However, similar to the findings reported by other authors,12 the majority of the cases in this study involved a single joint, with the knee occupying first place. A number of hypotheses have been proposed to explain this fact; however, the one most widely accepted is associated with hematogenous spread or the proximity of bacteria that penetrate the articular fluid because of the absence of a basement membrane in the synovial tissue following a knee injury or lesion.13

Among the clinical and epidemiological factors associated with the development of bacterial septic arthritis, we mentioned age, as up to 40% of the cases occur in adults over the age of 60 years.14 Among the risk factors that increase the probability of diagnosing an acute joint inflammation such as septic arthritis, those that are always included are age, history of diabetes mellitus, rheumatoid arthritis, recent joint surgery, joint replacement (synthetic material) and skin infection, among others.15

Although gender has been reported to be a factor of higher risk for certain specific types of septic arthritis, this aspect cannot be generalized. The majority of the individuals with septic arthritis in this study were men, a finding similar to those reported in previous studies.16

Another important factor in the development of septic arthritis is a history of an underlying rheumatic disease (lupus, osteoarthritis, rheumatoid arthritis or gout), principally in cases of polyarticular arthritis.17 In our study group, 13% of the cases were associated with osteoarthritis and 20% with rheumatoid arthritis. Binary logistic regression analysis revealed a statistically significant association for the presence of osteoarthritis. It has been pointed out that osteoarthritis, together with injuries,18 are a frequent cause of septic arthritis in patients over the age of 50 years,19 and more so if they are associated with the presence of autoimmune diseases,20 drug use and corticosteroids.18

Among the background features, the use of corticosteroids has been shown to be an important risk factor for the development of septic arthritis. We should not overlook the fact that the use of corticosteroids was established in previous studies and our patients were no exception.21

The etiology and clinical characteristics of septic arthritis are not easy to study, especially because it is difficult to establish an accurate bacteriological diagnosis in a large number of cases.22 The culture of the joint fluid is the gold standard for the diagnosis of infectious arthritis, with a sensitivity that ranges from 75% to 97%.23–25 In this respect, the microbiological pattern of septic arthritis has not changed much, and in recent decades, the majority of the researchers continue to highlight S. aureus and Streptococcus as the major causative agents,3,16 mainly because bacterial colonization is favored when there is tissue damage, which exposes the synovial membrane to contamination.26,27

In most hospitals, the evaluation of an inflamed joint can be carried out in a simple manner, with the examination of the synovial fluid, looking for crystals and bacteria, using a Gram stain, which has a sensitivity of nearly 60%.28 In this study, 78% of the participants had a positive Gram stain which pointed to the diagnosis and made it possible to start antibiotic therapy in a timely fashion. This is the policy in the center in which we work, committed to the Mexican Guidelines for the Prevention, Diagnosis and Treatment of Acute Septic Arthritis in Children and Adults (IMSS-368-10).29

As reported by other authors, staphylococci and streptococci were the infectious agents most frequently isolated.30 There was little presence of gram-negative bacteria, as agents of that type were detected in only four cases. There was a notable absence of cases of gonococcal arthritis, in contrast to the situation reported in North America and Australia, where it is a common cause of septic arthritis in young adults.22,23 In contrast, in European countries, the incidence is very low, similar to the findings in our series.11 As a possible explanation for this circumstance, Hook et al. proposed the existence of variations in the capacity of Neisseria gonorrhoeae to cause joint damage in different geographical regions of the world, a hypothesis that has not yet been confirmed by any study.16,22,31 Recently, Oppegaard et al.32 have reported the high specificity (98%) of CD64 and procalcitonin for the diagnosis of infectious diseases, including septic arthritis. As yet we have no experience in this regard in our setting and the possibility of including these diagnostic tests among others that could be utilized for the analysis of septic arthritis remains open.

A detailed clinical history and well performed physical examination are sufficient to awaken the suspicion of septic arthritis within the first 3 days of onset of symptoms in the majority of cases.33 In this respect, swelling, the presence of pain and functional limitation were the most prevalent clinical signs in our population and, in the logistic regression model, were clinical manifestations that enabled us to reach the diagnosis. Eder et al.8 and, somewhat later, Margaretten et al.10 reported pain to be a consistent symptom in up to 85% of the patients with septic arthritis. However, the individual differences in pain threshold can influence the final diagnosis. This was made clearer in a study performed by Burgos-Vargas et al. in 1210 patients with septic arthritis in which the objective was to predict the diagnosis of septic arthritis using a multivariate analysis that included pain (scored according to a visual analog scale), functional disability and the use of nonsteroidal anti-inflammatory drugs. At the end of the study, the diagnosis was based on a pain score of 5.2 or higher out of 10 possible points (maximum pain)34; thus, the authors conclude that, during the clinical evaluation of a painful, inflamed joint, a thorough analysis of all the signs in the inflamed joint would point toward the diagnosis and make it possible to rule out other possible causes of nonseptic arthritis.

Functional limitation continues to be a relevant clinical sign in septic arthritis. Our study found a prevalence of 51%; previous studies report values that range from 10% to 73%, in which the patient characteristics, type of bacterium, a correct and timely diagnosis and the treatment received had a direct influence on its development.16 Logistic regression analysis revealed a significant increase in the risk for swelling and functional limitation as important factors in the diagnosis of septic arthritis. This information agrees with the idea that the finding of a swollen, inflamed, reddened and overly warm joint is reason enough to include septic arthritis in the differential diagnosis of a joint disease.3 In our results, we observed no significant differences for the increase in the local temperature or hyperthermia, a fact that could be more due to the samples size of our study population than to a lack of statistical association.

In the case of fever, Margaretten et al. report that it has a low sensitivity (57%) for the diagnosis of septic arthritis10; consequently, it is considered to be a symptom of low specificity for the majority of conditions involving joints.35–37

Finally, synovial biopsy is known to be of no use in the diagnosis of acute bacterial arthritis; however, when an unclear diagnosis is suspected, it is common for the physician to perform a biopsy in cases of chronicity of the inflammatory signs, and in agreement with the clinical history of the patient in cases of amyloidosis, sarcoidosis or suspected metastatic tumors.38 In our center, it is performed only in patients who do not respond to medical treatment, when there is some doubt concerning the diagnosis or chronicity of the clinical picture, as we mentioned above.

This study has a number of limitations: it was carried out in a single center, the sample size, the cross-sectional (but not prospective) design, the fact that it was not possible to perform a cytological analysis of the synovial fluid in every case, an analysis was not done with additional tests for other diseases associated with septic arthritis in the group of individuals with negative bacterial culture, it was not possible to carry out a follow-up of the treatment and of the complications because many patients were lost to follow-up in our center when they returned to the municipalities from which they had been referred. However, the exclusion of synovial fluids considered to be contaminated and the methodology utilized allow us to suppose that the number of cases studied is representative of the region and that the findings can be applied to other areas or hospitals in which the population is similar. Moreover, it lends support to the results of previous studies in terms of the risk factors and clinical characteristics of septic arthritis.

In conclusion, as has been reported by other researchers, the most common clinical presentation of septic arthritis continues to be monoarthritis of the knee, associated with gram-positive bacteria, in which evidence of an inflamed, reddened and overly warm joint is reason enough to consider this diagnosis. Additional prospective studies will be required to further evaluate the course, treatment and complications of septic arthritis in Mexican patients.

The authors declare that they have no conflicts of interest.