The clinical spectrum and antibiotic sensitivity patterns of staphylococcal pyodermas in the community and hospital.

CONTEXT: The uncontrolled use of antibiotics has resulted in a relentless spread of multiresistant strains of Staphylococcus aureus. There are studies conducted in medical colleges in Chandigarh, Chennai, Mumbai and Vellore comparing pyodermas in the community and hospital setting based on clinical and bacteriological parameters. AIMS: This study, conducted over 1½ years from March 2009 to August 2010, aimed at analyzing the clinical spectrum and antibiotic sensitivity pattern of community and hospital-associated (HA) staphylococcal pyoderma. It also assessed the prevalence of methicillin-resistant S. aureus (MRSA) in the community and hospital cohort settings. SUBJECTS AND METHODS: The study comprised of 200 cases of staphylococcal pyodermas, derived from the community (150 cases) and hospital (50 cases). Patients were evaluated based on their clinical presentation; antibiotic susceptibility was tested using the Kirby-Bauer disk diffusion method. STATISTICAL ANALYSIS USED: Statistical significance between individual attributes between the community and HA staphylococcal pyoderma groups was analyzed using Chi-square test and mean differences using student's t-test.
RESULTS: Factors associated with community-associated (CA) pyodermas were young age (P = 0.0021), primary pyodermas, and involvement of extremities, while those with HA pyodermas were middle age, secondary pyodermas, and significantly increased body surface involvement (P = 0.041). Incidence of CA-MRSA was 11.3%, while that of HA-MRSA was 18%.
CONCLUSIONS: A high level of resistance to first-line drugs such as penicillin, ciprofloxacin and cotrimoxazole was observed, more so in the hospital strain than in the community strain. S. aureus demonstrated good susceptibility to cephalosporins. Though the two strains of MRSA differed clinically, they showed 100% sensitivity to vancomycin and linezolid.

What was known?

S. aureusis resistant to first-line drugs such as penicillin, ciprofloxacin, andcotrimoxazole but demonstrated consistently high sensitivity patterns for all cephalosporins.

Community-associated pyodermas were seen in young age, primary pyodermas, and involvement of extremities. The HA pyodermas were related to middle age, secondary pyodermas, and significantly increased body surface involvement.

MRSA strainswere isolated in a younger age group (27-29 years) in both study groups.

Introduction

There are numerous interacting causes of infection in any body tissue, many of which also aid in the persistence of the infection. Various organisms have been isolated and incriminated in pyoderma. Staphylococcus aureus and β-hemolytic streptococcus are the most common etiological agents.[12] Pyoderma, commonly caused by S. aureus, accounts for up to 17% of clinical visits in dermatological practice.[3] S. aureus often colonizes hospitalized as well as healthy people without any sign of infection. The preferential sites of colonization are anterior nares, perineum, axilla, and web spaces and these sites may act as reservoirs.[4]

Most strains of S. aureus are encountered in patients and carriers outside hospitals, and around 90% of those found in hospitals are now resistant to penicillin. This resistance is due to the ability of the microorganism to produce penicillinase, a β-lactamase. These organisms also show cross-resistance to other penicillins such as ampicillin, amoxicillin, carbenicillin, azlocillin, and piperacillin.[5]

Methicillin-resistant S. aureus (MRSA) is notorious in causing serious infection among hospitalized patients, with outbreaks of such infections posing a major problem in therapy and infection control.[678] Outbreak reports of MRSA are available from the Veteran Affairs Medical Center of Long Beach, CA, USA; and hospitals in Australia, France, Saudi Arabia, South Africa, and the UK.[678910] Hospitals in these countries report MRSA infections between 20% and 65% in domiciliary and intensive care settings.[678] A gradual reduction in MRSA infection acquisition rate was noted over a 12-month period following daily clinical laboratory surveillance, monthly prospective microbiology surveys of high-risk inpatients, and the recognition of previously infected patients.[7] Unlike nosocomial or hospital-associated MRSA (HA-MRSA) isolates, community-associated MRSA (CA-MRSA) isolates from patients without known MRSA risk factors, patients with open wounds, visitors or relatives of infected patients, healthcare personnel, IV drug abusers, immunodeficient patients, are generally multidrug susceptible. Multidrug resistance may develop rapidly with indiscriminate and inappropriate antibiotic use.[9]

Data from national nosocomial infection surveillance study from centre of disease control and prevention show that S. aureus infection had increased to 54.5% in 2000.[10] In India, MRSA prevalence overall increased from 12% in 1992 to 80.83% in 1997.[11] Owing to the epidemiological and genomic differences including antibiotic resistance between HA-MRSA and CA-MRSA infecting organisms, strategies to prevent and treat these infections understandably differ.[12]

This study compares the clinical and antibiotic spectra of staphylococcal pyodermas in HA-MRSA and CA-MRSA, derives the prevalence of the infection in study cohorts presenting to an out-patient and in-patient facility in a medical college. It presents the differences inpatient demographics, clinical features, and antibiotic susceptibility in both the study groups. As a corollary, a possible guide to empirical treatment of MRSA infections is provided based on the obtained antibiotic susceptibility.

Subjects and Methods

Clinical and bacteriological studies were conducted on patients with pyodermas and positive S. aureus isolates on culture. Two hundred cases of staphylococcal pyodermas were analyzed, of whom 150 were outpatients comprising the community-associated S. aureus pyoderma (CA-SAP) group. Fifty inpatients comprised the hospital-associated S. aureus pyoderma (HA-SAP) group. The sample size of both study groups was selected based on the frequency of encountering a patient with staphylococcal pyodermas, which were higher in the out-patient setting. Since a selection criterion was used for both study groups as outlined below, randomization was not required. The clinical investigator involved with interpretation of antibiotic susceptibility data was blinded to both study groups. The cross-sectional study was conducted over a period of 1½ years from March 2009 to August 2010 at the author's medical college based in Mangalore, Karnataka after obtaining clearance from the institutional ethical review board.

Inclusion criteria

For HA-SAP, the criteria were: (a) A history of hospitalization or surgery or dialysis such that infection was not present or incubating on admission in a patient hospitalized >48 h, or residence in long-term care facility within 1 year of study; (b) a permanent indwelling catheter or percutaneous medical device at the time of study; and (c) a positive culture for S. aureus, 48 h after admission.

For CA-SAP, a positive culture for S. aureus in patients without hospitalization in the past year and no antibiotic treatment in the previous month were the criteria. Patients attending the outpatient dermatology clinic would effectively represent the CA-MRSA group of the area served by the teaching hospital. Pyoderma caused by other bacteriological agents was effectively excluded.

Evaluation

A detailed history that elicited information on occupation, nutritional status, hygiene, duration of disease, and the co-existence of any other cutaneous or systemic disease was taken. General and system-specific examinations were conducted in all the patients. Lesions were classified into primary (pyoderma occurring without a predisposing cause or skin lesion) and secondary pyodermas (pyoderma in which an existing skin lesion becomes secondarily infected).

Microbiological examination

Specimen collection

Intact pustules were first cleaned with 70% alcohol. They were then ruptured with a sterile needle and the expressed pus was collected on two sterile cotton swabs. In case of ulcers and crusted lesions, normal saline was used to clean the wound, while the surrounding normal skin was cleaned with 70% alcohol. Two sterile swabs were rubbed over the expressed pus or the advancing edge of the ulcer.

Bacteriological methods

Gram's stain

Smears were prepared using pus from the first swab and were stained by Gram's method. They were examined for the type and number of bacteria.

Culture

The pus from the second swab was inoculated on blood agar and MacConkey's agar. The culture plates were aerobically inoculated at 37°C for 24-48 h. Colonies grown on the plate were identified by Gram's staining, colony morphology, and biochemical characteristics.

S. aureus colonies were identified using catalase test, coagulase test, oxidation fermentation (OF) test by Hugh Leifson's method, mannitol fermentation test, and urease test. Gram-positive cocci arranged in clusters with catalase positivity were further tested by coagulase test (slide and tube method), OF test, urease test, and mannitol fermentation. Those found positive for the above tests were identified as S. aureus.[5]

Antibiotic susceptibility testing for S. aureus

All S. aureus isolates were tested for their antibiotic susceptibility by Kirby–Bauer disk diffusion method using commercially available antibiotic disks (Himedia, Bombay, India; Beckton and Dickinson, Franklin Lakes, NJ, USA) according to Clinical and Laboratory Standard Institute guidelines.[13]

The antibiotics for which sensitivity was tested along with the disk content are illustrated in Table 1. The zone of inhibition was noted and interpreted using the Kirby–Bauer chart.[13]

Table 1

Antibiotic susceptibility

Detection of methicillin-resistant S. aureus

Methicillin resistance was detected using oxacillin and cefoxitin. Those having a zone of inhibition ≤10 mm for oxacillin and ≤19 mm for cefoxitin were further subjected to a minimum inhibitory concentration (MIC) test. The strains having MIC of ≥4 mcg/ml for oxacillin and ≥4 mcg/ml for cefoxitin were considered resistant to methicillin (MRSA) [Figure 1].[13] The susceptibility of these strains to second-line antibiotics, vancomycin and linezolid, was tested.

Figure 1

MRSA - Resistance to Oxacillin (ox) and Cefoxitin (Cn)

Statistical analysis

Statistical analyses were performed with SPSS for Windows (SPSS; SPSS Inc., Chicago, IL, USA). A test for significance of individual attributes in the clinical spectrum and antibiotic sensitivity pattern of CA and HA staphylococcal pyoderma was conducted using Chi-square test. Student's t-test was used to calculate mean differences of each individual attributes such as age, body surface area between the CA and HA staphylococcal pyoderma groups. Significance was indicated by a two-tailed P < 0.05.

Results

The mean age of the patients was 33.19 ± 19 years (range: 19-90 years) with a median age of 32 years. The mean age of the CA-SAP group was 30.8 years with a median age of 28 years. The mean age of the HA-SAP group was 40.57 with a median age of 47 years. There was a statistical difference in the mean value of patient's age between the two groups (P = 0.0021). The male to female ratio was 1:0.67 for the CA cases and 1:0.61 for the HA cases, indicating that both groups were well matched in sex distribution. Pre-schoolers, students, and skilled workers formed the majority of cases in the community group, whereas the number of housewives, businessmen, and infants was significantly more in the hospital group [Table 2].

Table 2

Classification of patients

Poor personal hygiene was seen in 15 (10%) of the community cases, whereas there was only one such case in the hospital group. Primary pyodermas constituted majority of the CA-SAP group with 79 (52.66%) cases, whereas secondary pyodermas were common in the HA-SAP group with 28 (56%) cases [Table 3]. In the CA-SAP group, the primary pyodermas were constituted by folliculitis and furunculosis, whereas the secondary pyodermas included infected scabies and eczema. The HA-SAP group had a larger proportion of secondary pyodermas such as infected eczema, ulcers, toxic epidermal necrolysis, and infected burns [Figure 2]. Though most of the lesions were on the legs in both the groups, a significantly more body surface area involvement (P = 0.041) was seen in the HA-SAP group than in the CA-SAP group [9.67 ± 0.36 cm vs. 4.82 ± 0.17 cm] [Figure 3]. As shown in Figure 4 and Table 4, the CA pyodermas were more sensitive to most of the tested antibiotics than the HA staphylococcal pyodermas and conversely, the HA pyodermas were resistant to many of the tested drugs. Least sensitivity was observed to penicillin in both the groups [Figure 4 and Table 4], whereas maximum sensitivity was seen to oxacillin and cephalosporins. Cephalosporins demonstrated least resistance in both the groups. However, statistically significant resistance or sensitivity patterns were not noted when comparing both groups.

Table 3

Distribution of primary and secondary pyodermas

Figure 2

Clinical variants of pyoderma

Figure 3

Case of TEN with HA-MRSA

Figure 4

Antibiotic resistance to S. aureus

Table 4

Comparison of the susceptibility patterns of S.aureus with other studies on hospital- and community-associated pyoderma

Antibiotic sensitivity

The hospital group demonstrated higher resistance to antibiotics such as penicillin, cotrimoxazole, and ciprofloxacin on comparison with the community group [Table 4]. Though no statistically significant differences were present in the resistance patterns, ciprofloxacin resistance was higher in the hospital (60%) group than in the community (40%) group [Table 4 and Figure 4]. Table 4 also compares the results of this study against those of other studies and also reveals an increased resistance to antimicrobials such as cotrimoxazole and gentamicin.

This study additionally tested the susceptibility of S. aureus to amoxicillin–clavulanic acid and cephalosporins such as cefuroxime, cefotaxime, and cefixime. The antibiotic sensitivity patterns for all cephalosporins were consistent above 85%. However, amoxicillin–clavulanic acid had almost similar susceptibility patterns when compared with cotrimoxazole and ciprofloxacin, and lower susceptibility in comparison to cephalosporins [Table 4].

MRSA

Among the 150 community patients with S. aureus pyodermas, 133 (88.66%) were methicillin-sensitive S. aureus (MSSA) and 17 (11.33%) were MRSA. Among the 50 hospital patients, 41 (82%) were MSSA, whereas the rest 9 (18%) were MRSA [Table 5]. The total prevalence of MRSA from both the groups was 26 (13%). MRSA strains were isolated in a younger age group (27-29 years) in both study groups. CA-MRSA lesions were mostly those of infected scabies and folliculitis. HA-MRSA was isolated more frequently from lesions such as ulcers, burns, and eczema [Table 6]. Five patients with CA-MRSA had a history of similar lesions in other members of the community (scabies). There was no statistical difference in the mean of patient's age between the CA-MRSA and HA-MRSA groups.

Table 5

Categorization of methicillin-resistant S. aureus in the study groups

Table 6

Characteristics of CA-MRSA versus HA-MRSA

The distribution of the lesions was predominant on the legs in the CA-MRSA group and widespread in the HA-MRSA group. Though 100% resistant to all first-line antibiotics, both the strains were 100% sensitive to vancomycin and linezolid. Two patients with HA-MRSA succumbed to the infection despite treatment with vancomycin.

Discussion

The skin infections caused by S. aureus range from primary infections such as impetigo, ecthyma, folliculitis, furunculosis, carbuncle, and sycosis barbae to secondary infections such as eczema, infestations, and ulcers. Mucin appears to be the critical surface that is colonized in a process involving interactions between staphylococcal protein and mucin carbohydrate.[14] Resistance to penicillin was noted within 4 years of introduction of penicillin and was due to the production of enzymes called β-lactamase (penicillinase) by previously susceptible bacteria.[1] Methicillin, the first β-lactamase stable semi-synthetic penicillin was introduced in 1960.[8] Resistance was detected within a year of its introduction.[115] MRSA strains are resistant to allb-lactam antibiotics.[19] In the last decade, the prevalence of resistance to penicillin G among isolates of S. aureus and Staph. epidermidis has consistently exceeded 90%.[16] Resistance to penicillin G is due to the production of β-lactamases under the control of transmissible plasmids and can be overcome with β-lactamase-resistant (second generation) penicillins such as nafcillin or methicillin.[17] For most other antibiotics, resistance develops in a multistep process during the course of multiple exchanges of the organism between patients and carriers. The staphylococci with multiple drug resistance, typically seen in a hospital setting, are known as “hospital-associated Staphylococcus.”[18]

There has been a gradual trend of increasing antibiotic resistance over the years. In the community group of staphylococcal infections, Ohana demonstrated a higher susceptibility to erythromycin and gentamicin as compared to that observed in this study.[19] Penicillin demonstrated highest resistance in this study, similar to the findings reported by Patil and Nagaraju [Table 4].[2202122]

The hospital group generally showed a higher resistance to first-line antibiotics when compared to the community group. Though no statistically significant differences were present in the resistance patterns, ciprofloxacin resistance was observed more in the hospital (60%) group than in the community (40%).

The multidrug resistance characterizing the nosocomial strains may be a result of the exposure of S. aureus to multiple antibiotics.[23] Antibiotics like erythromycin which constitute the first-line drugs against many infections are becoming increasingly ineffective.[24] Table 4, which compares results of various studies in relation to this study, reveals an increased resistance to cotrimoxazole and gentamicin.

Community-associated MRSA

Recent reports conclude that strains of MRSA have become established in the community across the world. Unlikely to have been derived from hospitals, these strains represent a widespread community MRSA infiltrating the hospital-setups[25] Unlike nosocomial MRSA isolates, community acquired strains from patients without known MRSA risk factors are generally multidrug susceptible (except to b-lactams) and have distinctive molecular characteristics. Their resistance is usually limited to methicillin. Saracolatz found MRSA to be endemic in Detroit, USA, accounting for 38% of all community acquired S. aureus infections.[26] Ohana reported the incidence of MRSA in community acquired S. aureus skin infections to be as low as 1% in Afula, Israel.[19] In a study in New Zealand, Riley reported 10% of all community acquired S. aureus infections to be caused by MRSA.[27] Of concern is the recent identification of strains of S. aureus with intermediate level resistance to vancomycin, the drug of choice for MRSA.[28] CA-MRSA is pauci-resistant and more polyclonal. It produces skin diseases and severe pneumonia in otherwise healthy people.[29]

Differences between CA-MRSA and HA-MRSA

HA-MRSA infections are well known. In 1982, an American hospital outbreak reported an incidence of 30% MRSA.[30] Studies conducted in Japan reported an incidence of about 41.5%.[31] There are many reports of increasing resistance of S. aureus from India.[3233] Methicillin resistance was seen in 40.47% among hospital-acquired skin infection in a South Indian study.[24] This study demonstrated its prevalence to be 11.33% in the community and 18% in the hospital group, comparable to rates published by Nagaraju and Thankiwale.[212234] Both the CA-MRSA and HA-MRSA were associated more with secondary pyoderma (64.9% and 87%, respectively) in our study. Also, 60% of the CA-MRSA isolates were from lesions of scabies and folliculitis, whereas HA-MRSA was isolated predominantly from ulcers, eczemas, and erosions (89%).

The risk factors for acquiring CA-MRSA include infancy, history of similar lesions in the community, chronic illnesses, prison-hood, athletes, and people with homosexual orientations.[22] In this study, 29% of the CA-MRSA patients were identified to have the first two risk factors.

Therapy for treating infections due to MRSA is often limited to glycopeptide antibiotics like vancomycin or the newly approved drugs such as linezolid and quinupristin/dalfopristin.[1] Reports of reduced susceptibility to vancomycin are posing a great threat to the viability of the available treatment options.[1] There have been reports of hetero-vancomycin intermediate S. aureus, subpopulations with reduced susceptibility within the strains with an MIC within the susceptible range of ≤4 μg/ml.[35]

Clinically, the CA pyodermas were commonly primary infections, occurring more frequently in young adults and over the extremities. HA pyodermas were more often secondary pyodermas in middle-aged patients and were characterized by a larger surface area of involvement.

An alarming resistance pattern was noted to commonly used antibiotics in this study. Amoxiclav has a mid-range susceptibility pattern similar to cotrimoxazole and ciprofloxacin. A strong sensitivity pattern to cephalosporins was seen. Prevalence of MRSA isolated from community was 11.3% (CA-MRSA) and nosocomial was 18% (HA-MRSA), with an overall prevalence of MRSA was 13%. Phakade found no MRSA in 619 cases of CA-SAP in a study conducted at KEM Hospital, Mumbai, India, whereas 45% of HA-SAP was methicillinresistant.[41] The prevalence of HA-MRSA in our study was found to be lower than other reports, but that of CA-MRSA was found concordant with reported series [Table 7]. Tiwari reported a prevalence of HA-MRSA isolated from tissue fluids in a tertiary hospital in Bhubaneshwar, India, the maximum 45% was from pus. MRSA strains were having 100% sensitivity to vancomycin and linezolid as noted by us in our study and 92.9% sensitivity to teicoplanin.[42] Fatality due to MRSA among 200 cases of pyoderma in our study was 1%. These patients belonged to the HA-MRSA group and succumbed to MRSA infection despite treatment with vancomycin. Septicemia and multiorgan failure had set in before the institution of susceptible antibiotic in them.

Table 7

Prevalence of methicillin-resistant S. aureus

In order to reduce the problem of antibiotic resistance, it is mandatory to survey and screen clinical isolates for resistance. This is necessary in situations of staphylococcal outbreaks inclosed surroundings (MRSA or MSSA infections in a critical care environment or high dependency domiciliary centers as in old-age homes). Isolates can be obtained from the axilla, nasal cavity, groin, perineum, and throat.[678] However, it may not be practical in an out-patient setting. Efforts must then be channeled toward prudent antibiotic use based on maximal field susceptibility in a given locality, as documented in this study, and by minimizing confounding factors for the development and persistence of infection.

What is new?

Fatality due to MRSA among 200 cases of pyoderma in our study was 1%.

These patients belonged to the HA-MRSA group and succumbed to MRSA infection despite treatment with vancomycin.