SKIN AND SOFT TISSUE INFECTIONS (SSTIs)
Learning Objectives: ● Identify signs and symptoms that may indicate a SSTI ● List common causative organisms and risk factors for SSTIs ● Distinguish between antibacterial treatments for SSTIs in the organisms they cover ● Describe supportive therapies that may be indicated in treatment of SSTIs
Patient Case: Chief Complaint: “I have a boil on my butt, and I cannot sit down for class.”
HPI: Jimmie Chipwood is a 19-year-old college student who presents to the ED with a new-onset “boil” on his right buttock. He noticed some pain and irritation in the right buttock area over the past week, but thought it was due to having slid into second base during a baseball game. The pain gradually increased over the next few days, and he went to the student health center, where they cleaned the wound and gave him a prescription for clindamycin 300 mg QID for 7 days. They recommended he try to keep the area covered until the antibiotic began to work. Today, Jimmie returned to the student health center for further evaluation and was referred to the ED for further care for his continued SSTI. At the ED, Jimmie says the area on his buttock is worse, and he cannot sit down for class. He reports only partial adherence to the clindamycin regimen, because he often forgets to take it and says it makes him nauseous.
PMH: Right gluteal skin and soft tissue infection, diagnosed approximately 1 week ago (Rx for clindamycin was given, but the patient reports nonadherence); 2010--appendectomy; 2012--repair of left ACL
Meds: Prescription ● Clindamycin 300 mg PO QID × 7 days (prescribed at student health center visit 1 week ago; patient did not complete full course). Allergies ● Penicillin (hives as a child). Immunizations ● Up-to-date per student health center records
SH: Denies any alcohol or illicit drug use.
This patient has a SSTI. Think about what you already know about SSTIs and how these case details relate. What are your initial thoughts for treating this patient?
Background ● SSTIs are infections involving any or all layers of the skin (epidermis, dermis, subcutaneous fat), fascia, and muscle, and they can remain local or spread far from the initial site of infection, leading to more severe complications ● Primary bacterial infections: usually involve areas of previously health skin and are caused by a single pathogen ● Secondary bacterial infections: occur in areas of previously damaged skin and are frequently polymicrobic ● Complicated SSTI: involve deeper skin structures (eg. fascia, muscle layers), require significant surgical intervention, or occur in patients with compromised immune function (eg. DM, HIV infection)
Pathophysiology: ● Human skin is host to an abundance of diverse bacteria and fungi (main SSTI causes are staph and strep), but several factors act together to confer protection against skin infections (eg. continuous epidermal renewal, sebaceous secretions) ● Conditions that may predispose a patient to the development of SSTIs: ○ High concentrations of bacteria (more than 105 microorganisms) ○ Excessive moisture of the skin ○ Inadequate blood supply ○ Availability of bacterial nutrients ○ Damage to the corneal layer allowing for bacterial penetrations (the best defense against SSTIs is intact skin!) ○ Uncontrolled diabetes (diabetic ulcers)
Types of SSTI ● Folliculitis, furuncles, and carbuncles: foliculitis is inflammation of the hair follicle and is caused by physical injury, chemical irritation, or infection; furuncles and carbuncles occur when a follicular infection extends to involve deeper areas of the skin (furuncle is a walled-off mass aka boil; carbuncle is a coalescence of furuncles, forming a single inflamed area) ● Erysipelas: distinct form of cellulitis involving the more superficial layers of the skin and cutaneous lymphatics ● Impetigo: superficial skin infection that is seen most commonly in children; categorized as bullous or nonbullous ● Lymphangitis: inflammation involving the subcutaneous lymphatic channels; characterized by red, linear streaks extending from the initial infection site toward the regional lymph nodes ● Cellulitis: acute infectious process that initially affects the epidermis and dermis and may spread subsequently within the superficial fascia ● Necrotizing soft-tissue infections: consist of a group of extremely severe infections, associated with high morbidity and mortality, requiring early and aggressive surgical debridement and appropriate antibiotics and intensive supportive care ● Diabetic foot infections: abscesses, cellulitis, or ulcers on the feet arising secondary to diabetes ● Pressure sores: ulcers caused by prolonged pressure against an area of skin; decubitus ulcer and bed sore are two types of pressure sores ● Animal and human bite wounds: associated with significant risk of infection without prompt attention to appropriate management
Signs and Symptoms: ● Vary widely depending on the category of SSTI ● Think pain, redness, warmth of an area of skin (lesions), which may or may not feature purulent or non-purulent abscesses ● Systemic signs of infection may or may not be present (eg fever, chills, malaise)
Gen: WDWN Caucasian male in no acute distress, but with noticeable pain when he walks and tries to sit VS: BP 129/74, P 96, RR 16, T 37.5°C; Wt 77.5 kg, Ht 6′0″ Skin: Right gluteal area: red, erythematous, warm, and tender to touch; localized fluid collection that appears fluctuant, consistent with a carbuncle and surrounding erythema HEENT: PERRLA; EOMI, oropharynx clear Neck/Lymph Nodes: Supple, no lymphadenopathy Lungs/Thorax: CTA, no rales or wheezing CV: RRR, no MRG Abd: Soft, NT/ND; (+) BS Genit/Rect: Large 2 cm × 4 cm red swollen area over the right buttock, with a localized fluid collection and surrounding erythema Extremities: Upper extremities: WNL; Lower extremities: could not be adequately assessed due to patient’s inability to sit; 2+ pulses bilaterally Neuro: A & O × 3 What signs and symptoms of the patient reinforce the diagnosis? What other information would you like to have to help you formulate a treatment plan?
Diagnosis and determination of organisms: ● Diagnosis often made on the basis of characteristic lesion(s) ● For certain types of SSTI, cultures should be collected if possible (eg. impetigo; cellulitis; DBI; pressure sores (from biopsy or fluid obtained by needle aspiration); animal bites showing signs of infection; otherwise complicated SSTIs), but diagnosis is still frequently made on clinical grounds rather than by culture ● Blood cultures may be useful (eg cellulitis, where bacteremia may be present in up to 30% of cases) ● When there is a high risk of polymicrobic infection (eg. cellulitis, DBI, animal bites), wounds should be cultured for aerobic and anaerobic organisms
Labs NA 138 mEq/L Hgb 15.5 g/dL WBC 11.3 x 103/mm3
K 3.2 mEq/L Hct 44% Neutros 89% Cl 98 mEq/L Plt 279 x 103/mm3 Lymphs 10%
CO2 23 mEq/L Monos 1%
BUN 33 mg/dL
SCr 0.9 mg/dL
Glu 95 mg/dL
Ca 9.4 mg/dL Urine Drug Screen (-) Alcohol, (-) marijuana, (-) cocaine and other substances
How might labs influence your treatment plan? Is there concern that this patient may have a systemic infection? How can you tell?
Treatment ● Considerations ○ Determine presence of signs of systemic illness ○ Supportive care ■ For mild infections, minimal; may include painkillers for pain and/or antipyretics for mild fever ■ For more serious infections involving extensive surgical debridement, more intensive care may be warranted; may include IV fluids ● Antimicrobial agents ○ Empiric antibiotic use for mild, uncomplicated SSTIs is appropriate (many SSTI diagnoses and treatments take place in the outpatient setting) ○ In an inpatient setting, empiric antibiotic use once cultures have been sent (if cultures are appropriate) ○ Narrow (or potentially broaden) therapy once results of cultures are known ○ Typical duration of therapy is 5 to 10 days, but is individualized per patient ● Incision and drainage (I&D) ○ Often employed for mild purulent infections, sometimes even without systemic antibiotic therapy when no signs of a systemic infection ○ Plays a role in more complicated or sever SSTIs as well, accompanied by antibiotic therapy ● Monitoring ○ WBC - for resolution of infection if initially elevated ○ Clinical stability ○ Fever and other signs of systemic infection ○ Resolution of symptoms (eg. pain, redness, swelling) of the site of infection Likely Organisms
General treatment recommendations and dosing ● See DiPiro Chapter 110
Recommended Oral Drugs for Outpatient Treatment of Mild-Moderate SSTIs
aMay be used in patients with penicillin allergy. bRecommended if CA-MRSA is suspected. cFluoroquinolone alone may be suitable for mild infections, while addition of drugs with antianaerobic activity may be recommended for more severe infections.
Treatment algorithm from the IDSA Guidelines
Figure 1. Purulent skin and soft tissue infections (SSTIs). Mild infection: for purulent SSTI, incision and drainage is indicated. Moderate infection: patients with purulent infection with systemic signs of infection. Severe infection: patients who have failed incision and drainage plus oral antibiotics or those with systemic signs of infection such as temperature >38°C, tachycardia (heart rate >90 beats per minute), tachypnea (respiratory rate >24 breaths per minute) or abnormal white blood cell count (<12 000 or <400 cells/μL), or immunocompromised patients. Nonpurulent SSTIs. Mild infection: typical cellulitis/erysipelas with no focus of purulence. Moderate infection: typical cellulitis/erysipelas with systemic signs of infection. Severe infection: patients who have failed oral antibiotic treatment or those with systemic signs of infection (as defined above under purulent infection), or those who are immunocompromised, or those with clinical signs of deeper infection such as bullae, skin sloughing, hypotension, or evidence of organ dysfunction. Two newer agents, tedizolid and dalbavancin, are also effective agents in SSTIs, including those caused by methicillin-resistant Staphylococcus aureus, and may be approved for this indication by June 2014. Abbreviations: C & S, culture and sensitivity; I & D, incision and drainage; MRSA, methicillin-resistant Staphylococcus aureus; MSSA, methicillin- susceptible Staphylococcus aureus; Rx, treatment; TMP/SMX, trimethoprim-sulfamethoxazole. Treatment Algorithm for Inpatient Treatment of Cellulitis
What drug, dose, route of therapy, dosing schedule, and duration of treatment should be used in this patient?
The patient was treated in the ED with I&D alone and was given wound care instructions. The fluid was not sent for culture and sensitivity. He returns to the ED 8 days later with a recurrent boil in the same right buttock area. On physical exam, the patient is found to have a new area of fluid collection (1 cm × 3 cm) and surrounding erythema. An MRI of the gluteal area was negative for deep tissue involvement and extension to other adjacent areas. Two sets of blood cultures were drawn and are pending, and a second I&D of the area was performed. The patient did have his nares and groin area swabbed for MRSA detection, but the results are pending. The patient has reported mild fevers without chills, but he has not taken his temperature at home. His current temperature is 37.7°C and all other vital signs are stable. Given the current information, the ED physician does not think Jimmie needs to be admitted. Was I&D alone an appropriate management strategy for the initial presentation of this patient case? Based on the above information, the patient has failed oral clindamycin (arguably) and an initial I&D. Does this patient need antibiotic therapy in addition to the second I&D and if so, what antimicrobial regimen would you now recommend for this patient?
References: ● Link to IDSA Guidelines: http://www.idsociety.org/Guidelines/Patient_Care/IDSA_Practice_Guidelines/Infections_ by_Organ_System/Skin_and_Soft_Tissue_Infections/ ○ Great for dosing and for additional specific antibiotic regimen choices for each type of SSTI ● Link to DiPiro Chapter 110: https://accesspharmacy-mhmedical- com.pitt.idm.oclc.org/content.aspx?sectionid=146071658&bookid=1861&Resultclick=2# 1145822838 ○ Key concepts in the beginning are an excellent overview, additional dosing information ● Link to DiPiro Casebook: https://accesspharmacy-mhmedical- com.pitt.idm.oclc.org/content.aspx?sectionid=155238395&bookid=2047&Resultclick=2# 1150076004