ANNALS of Internal Medicine

ANNALS of Internal Medicine AUGUST 1977 VOLUME 87 NUMBER 2 Published Monthly by the American College of Physicians Cutaneous Abscesses Anaerobic and Aerobic Bacteriology and Outpatient Management HARVEY W. MEISLIN, M.D.; STEPHEN A. LERNER, M.D.; MICHAEL H. GRAVES, B.S.; MICHAEL D. McGEHEE, M.D.; FRANK E. KOCKA, Ph.D.; JOSEPHINE A. MORELLO, Ph.D.; and PETER ROSEN, M.D.; Chicago, Illinois Specimens from 135 cutaneous abscesses in outpatients were cultured anaerobically and aerobically. Of these, 4% were sterile and 29% yielded pure cultures, predominantly of Staphylococcus aureus. Aerobic species were isolated from all anatomic areas. Anaerobes were found with a frequency comparable to aerobes in all nonperineal areas except the hand. In contrast, abscesses in the perineal region contained a greater variety and frequency of anaerobes. Only two patients were febrile. All abscesses were treated with incision and drainage, and all healed without complication, including those 74% that were treated without adjunctive antibiotics. Primary management of cutaneous abscesses should be incision and drainage. In general, routine culture and antibiotic therapy are not indicated for localized abscesses in patients with presumably normal host defenses. CUTANEOUS ABSCESSES are among the most frequently encountered soft tissue infections in acute treatment centers. About 2% of all patient visits to the adult emergency facility of The University of Chicago Hospitals and Clinics are for treatment of such abscesses. Despite the prevalence of cutaneous abscesses, there is little information on their bacteriology. In addition, recommendations on ideal management of these infections have not been uniform. From the Division of Emergency Medicine; the Department of Medicine, Section of Infectious Disease; the Clinical Microbiology Laboratories; and the Department of Pathology; the University of Chicago Pritzker School of Medicine; Chicago, Illinois. Anaerobic bacteria are known to be part of the normal flora of the skin and mucous membranes of man. The importance of anaerobes in intra-abdominal, respiratory, and central nervous system infections has been documented (1); however, their significance in cutaneous abscesses has not been thoroughly explored. This study was designed to investigate the anaerobic and aerobic bacteriology of cutaneous abscesses from various anatomic locations in outpatients. We expected this information to assist in developing a rational mode of management of these infections. Materials and Methods CLINICAL Patients presenting with cutaneous abscesses to the Emergency Department of the University of Chicago Hospitals and Clinics were evaluated for this study. A cutaneous abscess was defined as a localized collection of pus causing a fluctuant soft tissue swelling and surrounded by firm granulation tissue and erythema. Size generally varies with location and cause; however, all abscesses in patients under study had fluctuance at a minimum of 1 cm in diameter. Individuals admitted to the hospital for abscess treatment were excluded from the study; these included patients with evidence of systemic infection, those who were immunosuppressed, and those with serious underlying illnesses. Patients who were studied had a broad range of associated signs of infection, including local cellulitis, lymphangitis, regional adenopathy, or an elevated leukocyte count. The primary treatment for all abscesses was incision and drainage of the fluctuant area. The involved site was widely scrubbed with povidone-iodine (Betadine ) and surgically draped. After local anesthesia was obtained with 1% lidocaine or ethyl chloride spray, pus was collected for culture by percutaneous aspiration of the abscess cavity or by aspiration from Annals of Internal Medicine 87:145-149, 1977 145

Table 1. Characters zation of 135 Oi itpatient Abscessc is Anatomic Areas Abscesses Percent of Total Cultures Type of Bacterial Growth (Percent from Each Area) Bacterial per Abscess* No Aerobes Anaerobes Aerobes and Aerobes Anaerobes Growth Only Only Anaerobes average Head and neck 25 19 4 28 20 48 1 2 Trunk 11 8 0 45 18 36 1 2 Axilla 22 16 0 55 5 41 1 1 Extremity 16 12 19 44 13 25 1 1 Hand 8 6 25 63 0 13 2 0 Inguinal 7 5 0 29 57 14 0 3 Vulvovaginal 13 10 0 15 46 38 1 3 Buttock 12 9 0 33 33 33 1 3 Perirectal 21 16 0 0 33 67 1 5 * Cultures with no growth were excli tided. the cavity through the surgical incision. Each specimen was injected into an anaerobic transport tube that contained oxygen-free carbon dioxide and a few drops of mineral-salts buffer solution, and the tube was taken immediately to the laboratory for anaerobic and aerobic culture. The abscess cavity was completely drained, probed to remove loculations, irrigated with normal saline, loosely packed with a plain gauze wick, and dressed. The subsequent use of antibiotics was left to the discretion of each physician. Each wound was rechecked in 48 h, at which time the packing was removed. However, for facial abscesses the packing was removed at 24 h. Frequent warm soaks, elevation of the involved area, and daily rechecks were then continued until the wound showed signs of healing through cessation of drainage, formation of granulation tissue, and resolution of local tissue inflammation. At this time the patient was discharged from the study. The data were organized according to nine anatomic locations: head and neck (which excludes intraoral abscesses); trunk; axilla; extremity; hand; inguinal; vulvovaginal; buttocks (which includes pilonidal abscesses); and perirectal areas. For this study perineal area designates the general region between the thigh and waist and specifically includes the inguinal, vulvovaginal, buttock, and perirectal areas. BACTERIOLOGIC The specimens were processed immediately upon receipt in the Anaerobe Section of the Clinical Microbiology Laboratories. Smears of the specimens were Gram-stained in the conventional manner except that a 0.1% basic fuchsin counterstain was used instead of safranin. All abscess specimens were plated on eosin methylene blue agar, colistin-nalidixic acid agar, and chocolate agar (Bioquest; Cockeysville, Maryland) plates, and these were incubated at 35 C in 5% C0 2 and examined daily for 3 days. Aerobic and facultative bacteria were identified according to conventional methods (2) and grouped as aerobes for this study. Freshly prepared Schaedler agar (Bioquest) plates, containing vitamin K, and 5% laked sheep blood, with and without 50 jutg of gentamicin per ml, and colistin-nalidixic acid agar plates were inoculated with the specimen and incubated anaerobically at 35 C in GasPak jars (Bioquest). Roll-tubes with prereduced anaerobically sterilized brain-heart infusion agar (Difco; Detroit, Michigan) and tubes of chopped meat carbohydrate broth (Bioquest) were inoculated under exygen-free C0 2 using the methods in the Anaerobe Laboratory Manual of the Virginia Polytechnic Institute and State University (3). The anaerobic cultures in GasPak jars and roll-tubes were examined after 48 h and re-examined periodically for 2 weeks. Anaerobic bacteria were identified according to the procedures in the Anaerobe Laboratory Manual (3) and the Wadsworth Anaerobic Bacteriology Manual (4). To determine the prevalence of Proteus mirabilis in the head and neck, axilla, and trunk regions of the skin, these areas were swabbed for culture with saline-moistened swabs on each of 10 control outpatients without abscesses. Eosin methylene blue agar plates were inoculated with the swabs and incubated overnight at 35 C. These plates were then examined only for the presence of mirabilisy which was identified by conventional biochemical methods. Results CLINICAL INFORMATION Cultures were made of specimens obtained from a total of 135 abscesses in 133 patients. Eighty abscesses were in Table 2. Frequency of Isolation of Anaerobes fn am Each Area Anatomic Specimens Peptococcus Peptostreptococcus Clostridium Eubacterium Area < Of 7o Head and neck 25 56 0 0 0 Trunk 11 36 9 0 0 Axilla 22 31 9 0 5 Extremity 16 19 6 19* 6 Hand 8 13 0 0 0 Inguinal 7 57 57 0 0 Vulvovaginal 13 46 62 8 15 Buttock 12 50 25 8 0 Perirectal 21 67 57 10 29 * These isolates were all Clostridium perfringens. 146 August 1977 Annals of Internal Medicine Volume 87 Number 2

women and 55 in men. Only two patients had an oral temperature greater than 38.0 C. The average heart rate among patients in this series was 113.5/min, while the average heart rate among 100 afebrile patients without abscesses in the Emergency Department was 91.8/min. Of the buttock cultures, eight (67%) were from pilonidal abscesses. Abscesses in women were most commonly found in the axillary (20%), vulvovaginal (16%), perirectal (15%), head and neck (14%), and buttock (13%) areas. The most common sites of abscesses in men were the head and neck (26%), perirectal (16%), extremity (15%), inguinal (13%), and axillary (11%) areas. CULTURE RESULTS Bacteria were recovered from 96% of the abscesses. Of the 135 abscess specimens, only six (4%) had no bacterial growth. Three of these sterile cultures were from extremities, two were from hands, and one was from a facial site. Two abscesses related to drug abuse were among the six without bacteria. As seen in Table 1, isolation of aerobic bacteria alone was the predominant bacteriologic pattern in specimens of the trunk, axilla, extremity, and hand. At least one third of cultures from each of the areas in the perineal region contained anaerobes alone. Mixed cultures of aerobic and anaerobic bacteria were obtained from all sites, but the highest incidence of such mixed cultures (67%) was from the perirectal area. The average number of aerobes and anaerobes per abscess recovered from the 129 abscesses containing bacteria is reported for each anatomic area in Table 1. Cultures of purulent material from all anatomic sites yielded about one aerobe per abscess. However, multiple anaerobes per abscess were obtained from the perineal region. Thirty-nine (29%) of the abscess cultures yielded only one organism. In these pure cultures, Staphylococcus aureus was the most common organism found (72%). Only three abscesses yielded pure cultures of a single anaerobe. Table 2 records the major types of anaerobic bacteria isolated from abscesses of the various anatomic regions. Table 3 lists the incidence of various aerobic and facultative bacteria found in abscesses. Staphylococcus aureus was present in 32 abscesses (24% of the total), and in 28 (21 % of the total) it was the only organism isolated. Of the 32 isolates of Staphylococcus aureus, only one (3%) was susceptible to penicillin G. Among Gram-negative aerobes, only P. mirabilis was isolated frequently. Fifteen of 16 isolates were associated with anaerobic cocci. Proteus mirabilis was found predominantly in the trunk and axilla but never in the perineal area. Among the 30 specimens obtained from three skin sites of 10 control outpatients, there was only one isolate of P. Mirabilis, which was from an axilla. GRAM-STAINED SMEARS The culture confirmed the interpretation of morphotypes in the corresponding Gram-stained smears for 74% of the 110 abscess specimens examined microscopically. Twenty-seven specimens had only large "grapelike" clusters of Gram-positive cocci in the smear. Of these, 24 (89%) yielded 5. aureus in pure culture. The other three abscesses with such a smear contained either Staphylococcus epidermidis or peptococcus. None of the sterile abscesses had a positive smear. Of the specimens with positive cultures, 6% of those whose smears were examined had no discernible bacteria. Discussion There were similarities in the microbial composition among abscesses in the perineal region (inguinal, vulvovaginal, buttock, and perirectal areas). These generally included organisms found in stool. On the other hand, bacteria from abscesses in areas more remote from the rectum were primarily constituents of the microflora indigenous to the skin. The presence of multiple anaerobic species was characteristic of abscesses from the perineal region, while only about one anaerobe per abscess was present in nonperineal abscesses. Mixed infections with anaerobes and aerobes were seen about as frequently in abscesses of the perineal region as elsewhere, but the presence of anaerobes without aerobes was more typical of perineal infections. Certain members of the complex fecal flora (5) were cultured more frequently from abscesses. Bacteroides was a far more common constituent of abscesses from the perineal region than of other abscesses. Bacteroides fragilisy the most numerous Gram-negative species in human feces (5), is the only anaerobe commonly resistant to Tabte 2. (Continued) Propionibacterium Lactobacillus Bacteroides Bacteroides Bacteroides Other Fusobacterium melaninogenicus corrodens fragilis Bacteroides 4 % > 28 0 8 8 4 8 0 36 0 18 9 9 9 9 14 0 5 0 5 0 0 o 6 f\ n n ii o 0 0 0 0 0 0 0 0 29 57 29 0 29 14 8 23 39 31 23 23 46 0 25 58 33 17 25 25 5 14 81 57 47 29 43 Meislin et al Cutaneous Abscesses 147

Table 3. Frequency of Isolation of Aerobes from Each Area Anatomic Specimens Staphylococcus Staphylococcus Beta-Hemolytic Area aureus epidermidis Streptococcus (Group A and B) Of Head and neck 4 Trunk 11 18 18 0 25 < 16 /c 24 Axilla 22 50 9 0 Extremity 16 38 6 6 Hand 8 25 38 38 Inguinal 7 29 0 0 Vulvovaginal 13 8 0 8 Buttock 12 33 0 8 Perirectal 21 0 5 5 penicillin (6). This species was found less frequently in abscesses in each of the anatomic areas comprising the perineal region than was Bacteroides corrodens, which has been considered more characteristic of the oral, rather than fecal, microflora (5). Bacteroides melaninogenicus, which occurs in stool as well as the oral cavity (5, 7), was the most commonly isolated species of bacteroides. If feces are the major source of bacteria for superficial abscesses of the perineal region, then local conditions apparently favor the proliferation in abscesses of B. melaninogenicus and B. corrodens more than B. fragilis. This predominance contrasts with data from intra-abdominal abscesses resulting from fecal contamination, in which B. fragilis is the major Gram-negative anaerobic bacillus (8, 9). The presence of B. melaninogenicus in the normal vaginal flora may also contribute to its predominance in abscesses of the perineal region. Peptococci and peptostreptococci, both anaerobic Gram-positive cocci, are also fecal constituents. They were isolated as frequently from abscesses of the perineal region as Bacteroides organisms. These cocci have also been associated commonly with intra-abdominal abscesses (10). Peptococci, which reside among the skin flora as well as in feces (5), were frequently isolated from nonperineal cutaneous abscesses. As expected, peptostreptococci, which are less common on skin than in bowel or vaginal flora (5), were found less frequently in nonperineal infections. Clostridia, which are commonly found in feces and soil, were isolated infrequently from cutaneous abscesses. Clostridium perfringens was isolated only from extremities. The other clostridial isolates were from sites associated with fecal organisms (vulvovaginal, buttock, and perirectal areas). Alpha- and non-hemolytic streptococci, which are normal constituents of the fecal and oral flora, were the major aerobes in perirectal abscesses. In contrast, non- Group D beta-hemolytic streptococci, which are generally absent from feces, appeared most often in abscesses of the hand. Proteus mirabilis was found almost exclusively in abscesses of the trunk, axilla, and head and neck but was absent from the perineal region, despite its presence in fecal flora (11). The source of this organism is not clear, since skin cultures from 10 control patients confirmed Vass' report of the infrequency of isolation of P. mirabilis from the skin (12). All other Enterobacteriaceae combined were isolated less frequently than P. mirabilis. Although Escherichia coli was occasionally cultured from perineal abscesses, the infrequency of its isolation was especially conspicuous because it is the most common aerobe in stool and in intra-abdominal abscesses (5, 9, 11). Staphylococcus aureus, the most prevalent aerobe, was found in all areas where abscesses originate on skin surfaces. These include all nonperineal abscesses as well as those from perineal areas other than vulvovaginal and perirectal. These latter two sites, where abscesses originate from adjacent mucous membranes rather than skin, had only a single isolate of 5. aureus. Contrary to general clinical impression, S. aureus was isolated in only 50% or less of abscesses from each site. Usually, it was found alone and rarely with other aerobes. This organism has a well-recognized propensity for abscess formation, both in local infections and in visceral infections resulting from hematogenous dissemination. In contrast to anaerobes (13-16), its potential for abscess formation is not as dependent on synergistic bacterial mixtures (17). Neisseria gonorrhoeae may invade vulval glands. However, its absence from the 13 vulvovaginal abscesses in our series is consistent with a low incidence of only 10% reported previously for such infections (18). Our results also confirm reports of a major involvement of peptostreptococci and other anaerobes in vulvovaginal abscesses (19). Elevation of the average heart rate over normal controls was associated with these cutaneous abscesses. However, fever greater than 38 C was seldom present, even though it was not a criterion for exclusion from the study. Parenteral drug abuse was an underlying factor for only a few abscesses in this entire series. However, these abscesses were all at sites of injection on extremities and constituted 38% of extremity abscesses. Two of the six specimens from drug abusers were sterile. Despite the absence of bacteria, these abscesses were as purulent and as extensive clinically as those infected with bacteria. Moreover, their course of development was more rapidly progressive from the onset. These clinical features may be due to the injection of necrotizing chemical irritants such 148 August 1977 Annals of Internal Medicine Volume 87 Number 2

Table 3. (Continued) Alpha and Corynebacterium Proteusmirabilis Enterobacteriaceae Non-Hemolytic (Other than P. mirabilis) Streptococcus (Diphtheroids) - - -- /o 8 8 12 12 9 0 36 0 9 5 31 9 6 13 6 13 0 0 13 13 14 0 0 14 21 0 0 8 17 25 0 0 48 10 0 10 as concentrated saline, which is used as a street therapy for drug overdose. All of the patients in this study were treated with incision and drainage. No adjunctive antibiotics were prescribed for 74% of the patients, even though some of the clinically more severe abscesses were in this group. The incidence of effective antibiotic therapy was probably even lower than 26%, since poor compliance with oral antibiotic regimens is common (20). All of the patients in the series improved clinically, without subsequent requirement for antibiotic treatment or repeat incision and drainage. In the high-risk patient, in one with signs of systemic infection, or in one with abscesses in areas of the face drained by the cavernous sinus, antibiotic therapy may be indicated. Analysis of the Gram-stained smear and correlation of the patient's abscess site with the bacteriologic data for similar anatomic sites presented in this study might permit a prediction of which organisms are present. With this information, one could presumptively initiate an appropriate antibiotic regimen. This study shows that incision and drainage alone should suffice in the treatment of localized cutaneous abscesses in patients with presumably normal host defenses. Thus, there is no indication for initial Gram-stain, culture, or antibiotic therapy for these patients. ACKNOWLEDGMENTS: Received 14 January 1977; revision accepted 14 May 1977. Requests for reprints should be addressed to Harvey W. Meislin, M.D.; Emergency Medicine Center, University of California, Los Angeles; Los Angeles, CA 90024. References 1. FINEGOLD SM, BARTLETT JG, CHOW AW, et al: Management of anaerobic infections. Ann Intern Med 83:375-389, 1975 2. LENNETTE EH, SPAULDING EH, TRUANT JP: Manual of Clinical Microbiology, 2nd ed. Washington, D.C., American Society for Microbiology, 1974 3. HOLDEMAN LV, MOORE WEC: Anaerobe Laboratory Manual, 3rd ed. Blacksburg, Virginia Polytechnic Institute and State University Anaerobe Laboratory, 1975 4. SUTTER VL, VARGO VL, FINEGOLD SM: Wadsworth Anaerobic Bacteriology Manual, 2nd ed. Los Angeles, Anaerobic Bacteriology Laboratory, Wadsworth Hospital Center, Veterans Administration, 1975 5. SMITH LD: The Pathogenic Anaerobic Bacteria, 2nd ed. Springfield, Illinois, Charles C Thomas, 1975 6. MARTIN WJ, GARDNER M, WASHINGTON J A II: In vitro susceptibility of anaerobic bacteria isolated from clinical specimens. Antimicrob Agents Chemother 1:148-158, 1972 7. GORBACH SL, MENDA KB, THADEPALLI H, et al: Anaerobic microflora of the cervix in healthy women. Am J Obstet Gynecol 117:1053-1055, 1973 8. SWENSON RM, LORBER B, MICHAELSON TC, et al: The bacteriology of intra-abdominal infections. Arch Surg 109:398-399, 1974 9. GORBACH SL, THADEPALLI H, NORSEN J: Anaerobic micro-organisms in intra-abdominal infections, in Anaerobic Bacteria: Role in Disease. Edited by BALOWS A, DEHAAN RM, DOWELL VR, GUZE LB. Springfield, Illinois, Charles C Thomas, 1974, pp. 399-407 10. MOORE WEC, CATO EP, HOLDEMAN LV: Anaerobic bacteria of the gastrointestinal flora and their occurrence in clinical infections. J Infect Dis 119:641-649, 1969 11. ATTEBERY HR, SUTTER VL, FINEGOLD SM: Normal human intestinal flora, in Anaerobic Bacteria: Role in Disease. See Reference 9, pp. 81-97 12. VASS JG: Effects of antimicrobial soap on the ecology of aerobic bacterial flora of the human skin. Appl Microbiol 30:551-556, 1975 13. HITE KE, LOCKE M, HESSELTINE HC: Synergism in experimental infections with nonsporulating anaerobic bacteria. / Infect Dis 84:1-9, 1949 14. HILL GB, OSTERHOUT S, PRATT PC: Liver abscess production by non-spore, forming anaerobic bacteria in a mouse model. Infect Immun 9:599-603, 1974 15. ONDERDONK AB, WEINSTEIN WM, SULLIVAN NM, et al: Experimental intra-abdominal abscesses in rats: quantitative bacteriology of infected animals. Infect Immun 10:1256-1259, 1974 16. ONDERDONK AB, LOUIE T, SULLIVAN-SIEGLER N, et al: Microbial synergy in experimental intra-abdominal abscesses. Infect Immun 13:22-26, 1976 17. WILSON GS, MILES AA: Topley and Wilson's Principles of Bacteriology and Immunity, 6th ed. Baltimore, Williams and Wilkins Co., 1975, pp. 764-801 18. GORBACH SL, BARTLETT JG: Anaerobic infections. N Engl J Med 290:1177-1184, 1974 19. SWENSON RM, MICHAELSON TC, Daly MJ, et al: Anaerobic bacterial infections of the female genital tract. Obstet Gynecol 42:538-541, 1973 20. BLACKWELL B: Drug therapy: patient compliance. N Engl J Med 289:249-252, 1973 Meislinetal Cutaneous Abscesses 149