Aeromonas as a Cause of Purulent Folliculitis: A Case Report and Review of the Literature

Abstract

Aeromonas species are rarely an identified cause of folliculitis. Here, we describe the case of a patient who had purulent folliculitis of the breast caused by an Aeromonas species and review 4 other cases presented in the literature, highlighting the commonalities observed. Aeromonas infection should be considered in patients who present with purulent folliculitis, particularly those with exposure to nonchlorinated pools or baths.

CASE REPORT

An 11-year-old girl with no significant past medical history developed warmth, swelling, tenderness, erythema, and pruritus of her left breast while traveling in the Dominican Republic. Five days into her trip, she felt a pinch-like pain in her left breast. Over the course of the next day, she developed fever, headache, and vomiting, and her left breast became warm, tender, and markedly swollen. She had no known trauma or insect bites during her trip, but she swam many times in an inflated pool filled with well water. On the sixth day of her trip, she was taken to a local emergency department because of worsening swelling and pruritus. An ultrasound of her breast did not reveal any drainable fluid collection, and laboratory results were notable for a white blood cell count of 15.3 × 10⁹ cells/L with 89% neutrophils. She was treated with penicillin and gentamicin and discharged home with a prescription for a topical anti-inflammatory spray.

Two days later, she returned to the United States and immediately presented to the emergency department with continued left breast pruritus and pain that was aggravated by left-arm movement. The physical examination revealed her left breast to be markedly swollen, warm, tender, and erythematous; an indurated violaceous region at the 2 o’clock position and blisters with straw-colored fluid over the inferior aspect were found. She was admitted and given intravenous antibiotics for apparent cellulitis. Shortly thereafter, she developed fever, tachycardia, and tachypnea concerning for systemic inflammatory response syndrome. She was started on empiric cefazolin and clindamycin, after which her vital signs stabilized quickly. Results of blood cultures and wound cultures of blister specimens were negative. After 4 days, the warmth, pain, and pruritus in her left breast had improved but not resolved completely, and she was discharged home to complete a 14-day course of clindamycin. A physical examination before discharge revealed that the erythema had improved markedly, but an 8-cm violaceous region with ruptured bullae inferiorly remained around the left breast (Figure 1A). The lesion lacked discharge, purulence, or bleeding.

Figure 1.

Gross and histologic views of inflammation in the patient’s breast. (A) Image of the patient’s breast taken at the time of discharge from her first hospitalization; marked edema, violaceous skin changes, and ruptured bullae can be seen. The inked outline shows where the erythema had extended at the time of admission 4 days earlier. (B) Hemotoxylin and eosin–stained image of the punch biopsy specimen, which revealed marked neutrophilic infiltrate with abscess formation around the hair follicle (arrows) and eccrine glands (arrowhead). The image was taken at ×10 magnification.

Over the next 2 weeks, the girl continued to complain of pain and pruritus of her left breast, which prompted another visit to the emergency department. An ultrasound examination again revealed no abscess formation. She was seen in the general surgery clinic, where her clindamycin was switched to trimethoprim-sulfamethoxazole. Because of the lack of improvement after 4 days, she ultimately was readmitted for further diagnostic evaluation. A repeat ultrasound examination of her breast revealed a minimal fluid collection that was too small to be aspirated. Punch biopsy specimens of her breast were obtained, and histology revealed folliculitis with a dense neutrophil infiltrate around the hair follicle and eccrine glands, a middermal abscess, and rare Gram-negative bacteria (Figure 1B). Results of Gram staining, a KOH prep, and cultures of the biopsy sample were negative for bacteria and fungi. After the punch biopsy, her left breast began to slowly drain purulent material through the biopsy site for the next 7 days. A culture of this pus grew an Aeromonas species that was sensitive to amikacin aztreonam, cefepime, ceftazidime, ciprofloxacin, gentamicin, meropenem, piperacillin-tazobactam, tobramycin, and trimethoprim-sulfamethoxazole and resistant to imipenem. Ciprofloxacin was added the day after her breast began draining. Her pain and pruritus began to improve with the drainage and ciprofloxacin treatment, and she was discharged home to finish a 14-day course of oral ciprofloxacin. Her pain and pruritus resolved completely by the end of the antibiotic course, and the skin discoloration on her left breast improved gradually over the next 4 months; some residual scarring and induration remained.

DISCUSSION

Aeromonas species are facultative anaerobic toxin-producing Gram-negative bacilli that typically are found worldwide in aquatic environments, including fresh or brackish water, marine environments, and drinking water [1, 2]. Aeromonas infections, which are caused most commonly by the phenospecies A hydrophila, A caviae, and A veronii biotype sobria, often result from bites of alligators, fish, leeches, or other aquatic animals that harbor Aeromonas species as part of their normal microbiota. Drinking contaminated water is also an important route of infection, particularly in low-income countries [1, 2].

The incidence of Aeromonas infection in California was estimated at 10.6 cases per 1 million population per year, but the rate might be lower in Europe [3, 4]. Although Aeromonas isolates are identified most frequently in gastrointestinal samples, whether Aeromonas is a causative agent of gastroenteritis remains controversial [3, 5]. Aeromonas infection most commonly presents as a skin and soft-tissue infection (SSTI). Other rare presentations include septicemia (often associated with malignancy or hepatobiliary disease), peritonitis, pneumonia, meningitis, and ocular infection [5]. Virulence factors include cytotoxins, enterotoxins, hemagglutinins, and exoenzymes, all of which contribute to disease pathogenesis [2].

Aeromonas-associated SSTIs can range from mild cellulitis to more severe deep-seated infections involving bone, joints, and/or muscles [1, 2]. Cellulitis caused by Aeromonas is commonly associated with medicinal leeches, but reports of such infection in healthy individuals with no predisposing factors is uncommon [5, 6]. In contrast, wound infections almost always result from a break in the skin (e.g., abrasion, penetrating trauma, burns) that becomes exposed to contaminated water or soil. More severe SSTIs are often associated with immunosuppression [7, 8].

Our patient improved initially while receiving cefazolin and clindamycin, antibiotics that are typically ineffective against Aeromonas species. Given that 60% to 70% of SSTIs after water exposure are polymicrobial in nature [1, 4], it is possible that our patient had a polymicrobial infection that involved an organism, such as a Staphylococcus or Streptococcus species, that was susceptible to these antibiotics. Her persistent symptoms and readmission were likely a result of the untreated Aeromonas infection. The lack of improvement while on trimethoprim-sulfamethoxazole—an agent to which her isolate was susceptible—was possibly related to the lack of adequate source control, an observation that underscores the importance of draining abscesses. In addition, it is interesting that the bacterial culture of her biopsy sample had no growth, which might have been a result of sampling error or the fact that viable organisms were present only in the abscess and not within the tissue itself.

In our patient, we found evidence of folliculitis from the pathology, clinical findings, and pathological findings of a suppurative infection and a wound culture that grew Aeromonas. Although Pseudomonas aeruginosa is a well-recognized cause of folliculitis associated with swimming pools and hot tubs, some limited precedence for Aeromonas as a cause of folliculitis exists (Table 1) [9, 10]. It is interesting to note that 2 of the 4 previously reported cases were associated with a contaminated home spa bath, and the other 2 cases were associated with an inflatable swimming pool [9, 10]. It is possible that our patient was exposed to Aeromonas while swimming in the well-water–filled pool in the Dominican Republic. It should be noted that more than 90% of the natural aquatic habitats sampled in the United States and Puerto Rico are contaminated with Aeromonas species. [11]. In addition to having a similar exposure history, all 5 patients had a pustular component that is consistent with Aeromonas-related SSTI. Indeed, a prospective study from France found that 74% of Aeromonas-associated SSTIs presented as a purulent wound infection, and 26% of total manifested as a soft-tissue abscess [4].

Table 1.

Known Cases of Folliculitis Caused by Aeromonas

Patient Demographics	Presentation	Suspected Source	Treatment	Outcome	Reference or Source
15-y-old girl, 13-y-old boy	Generalized pruritic, perifollicular erythematous macules and papules, some pustules	Inflatable swimming pool (Spain)	Topical 0.1% gentamicin cream for 1 wk	Symptom resolution without sequelae	9
34-y-old man, adult woman	Folliculitis, edema, and tender nodules in groin; fevers; purulent drainage	Home spa bath (Australia)	Oral ciprofloxacin for 6 wk	Symptom resolution, resulting cicatricial alopecia	10
11-y-old girl	Breast edema, tenderness and pruritus; violaceous skin appearance; fever and chills; purulent drainage	Inflatable swimming pool (Dominican Republic)	Oral ciprofloxacin for 14 days	Symptom resolution, scarring	This study

Despite these similarities, each of the cases differed slightly in appearance and presentation (Table 1) [9, 10]. Although our patient’s infection seemed clinically compatible with widespread cellulitis, the violaceous hue associated with her inflammation was particularly unusual and likely reflected underlying suppuration. In addition, our patient developed subsequent scarring, as did 2 of the patients in the literature. This scarring, along with the suppuration, likely reflects our patient’s delayed diagnosis and might represent the natural history of Aeromonas infection in an enclosed space. Results of pathology from our patient’s breast biopsy specimen confirmed the diagnosis of folliculitis, which is consistent with the fact that her most prominent complaint throughout her illness was that of pruritus—a hallmark of folliculitis. In our patient, clinical and pathologic findings consistent with purulent folliculitis ultimately were found; the superimposed cellulitis that was present initially improved with clindamycin, but this treatment did not help with the underlying Aeromonas infection. Given that Aeromonas species are almost universally resistant to penicillins and first-generation cephalosporins, infections with these bacteria should be treated with a fluoroquinolone, a third- or fourth-generation cephalosporin, or a carbapenem [2].

The true incidence of Aeromonas-related folliculitis remains unknown. It is likely that many of these water-associated cases are clinically diagnosed as a P aeruginosa infection and are either self-limited in nature or treated with an antibiotic, such as ciprofloxacin, that is active against both organisms. However, as exemplified by our case, Aeromonas species should be considered as a possible cause of severe cases of folliculitis, cellulitis, and/or abscesses that are associated with water, because the identification and timely treatment of this pathogen can result in improved outcomes.

Notes

Acknowledgements. N. K. S. is supported by National Institutes of Health award K08 AI108690. Birgitta Schmidt (Boston Children’s Hospital) assisted with obtaining the histology image.

Potential conflicts of interest. All authors: No reported conflicts.

All authors have submitted the ICMJE Form for Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.