Approach
Infection with community-associated MRSA is often diagnosed based on clinical suspicion, following review of the presenting history, risk factors, and physical examination. Healthcare-associated MRSA infection should similarly be suspected in patients with risk factors, prior history, and signs and symptoms consistent with an infectious process. The skin and other non-sterile body areas can be colonised without evidence of an infectious process. Culture and sensitivity is required to confirm the diagnosis of MRSA infection.[22] CDC: Methicillin-resistant Staphylococcus aureus (MRSA) Opens in new window
History
The history in any patient suspected of being infected with MRSA should include questioning about the presence of risk factors. Risk factors that are associated with MRSA infection include chronic illness requiring healthcare visits, living in crowded conditions/semi-closed communities, prior antibiotic use, previous history of MRSA infection, exposure to an MRSA-positive person, nasal colonisation with MRSA, and HIV infection. Specific risk factors strongly associated with healthcare-associated MRSA include older age groups (median age 64 years), recent hospitalisation, and presence of an indwelling device or current wound. Patient populations that have been significantly impacted by community-associated MRSA include children and younger adults (median age 22 years), Native Americans and Pacific islanders, men who have sex with men, amateur and professional athletes, individuals in correctional facilities, and intravenous drug users.
MRSA should be considered in patients presumed to have infections that are not responsive to penicillin antibiotics. This is especially true for skin and soft-tissue infections, which are the most common forms of MRSA infection.[3] Typical syndromes include the following patterns of infection.
Skin and soft-tissue infections
Patients often present with single or multiple skin lesions (e.g., boil) or pustules.
Patients may relate a history of a spider bite, without ever seeing a spider.
Prior history of MRSA should raise the level of suspicion.
Bacteraemia and sepsis
Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to an infection.[23]
Presentation of sepsis may range from non-specific or non-localised symptoms (e.g., feeling ill with a normal temperature), to severe signs with evidence of multiorgan dysfunction and septic shock. The threshold for clinical suspicion should be low.
See Sepsis in adults.
Endocarditis
Patients may present with fever, chills, shortness of breath, arthralgias, night sweats, and fatigue.
There may be a possible source of infection.
History of intravenous drug use or immunocompromised state should greatly raise the suspicion of MRSA.
Joint infection
Patients present with a history of a painful, swollen joint, which may involve a prior joint replacement.
Pneumonia
Patients present with fever, chills, cough, and shortness of breath.
Patients can be severely ill.
Urine infection
Patients may present with painful urination, haematuria, fever, altered mental status, chills, or urinary retention.
Patients with indwelling catheters may present with fever, chills, signs of bacteraemia, and possibly irritation or pain at the catheter site.
A history of urinary catheter use may be present.
When Staphylococcus aureus is isolated in the urine, an endovascular source of infection should be considered.
Physical examination
Skin and soft-tissue infection
Community-associated MRSA often presents as erythematous lesions or pustules, in single or multiple forms.
Skin lesions are often mistaken for an insect bite or folliculitis.
Abscess formation is possible.
Purulence, with or without the presence of a drainable abscess, is more likely to represent a staphylococcal infection, while cellulitis without purulence is more likely to be a streptococcal infection and may be associated with lymphangitic tracking.
Central ulceration is sometimes present. [Figure caption and citation for the preceding image starts]: A common ulcerative skin lesion secondary to MRSA on a patient's armPublic Health Image Library, CDC website [Citation ends].
[Figure caption and citation for the preceding image starts]: Cutaneous abscess caused by MRSAGregory Moran MD, from the Public Health Image Library, CDC website [Citation ends].
Bacteraemia and sepsis
Tachycardia, fever, hypotension that is refractory to intravenous fluids, cyanosis, bruising, or petechiae suggestive of disseminated intravascular coagulation and altered mental status may be present with MRSA bacteraemia.
Healthcare-associated MRSA, as compared with community-associated MRSA, can present as a more severe infection, such as septic shock.[24] However, severe cases of community-associated MRSA such as necrotising fasciitis, necrotising pneumonia, and Waterhouse-Friderichsen syndrome have been reported.
Patients with indwelling vascular catheters may present with fever, pain, erythema, or exudate at the site.
Endocarditis
Patients may present with fever, cardiac murmur, tachycardia, and signs of congestive heart failure.
Less commonly, there may be Roth spots (retinal haemorrhages), Janeway lesions (non-tender, small erythematous or haemorrhagic macular or nodular lesions on the palms or feet), or subungual splinter haemorrhages.
Joint infection
Pain, swelling, and warmth of the relevant joint may be present.
Fever accompanies the joint findings.
Pneumonia
Patients present with fever, tachypnoea, and respiratory distress.
Abnormal findings on pulmonary examination that suggest consolidation include dullness to percussion, or egophony or rales.
Healthcare-associated MRSA, as compared with community-associated MRSA, can present as a more severe infection, such as septic shock.[24] However, cases of fulminant and necrotising pneumonia have been reported with community-associated MRSA, particularly in young, otherwise healthy individuals.
Urine infection
Patients may present with abdominal pain, fever, and flank pain.
Peri-nephric abscess formation may also be seen.
Investigations
Skin and other non-sterile areas may be colonised with MRSA, but this does not necessarily mean the patient has an acute infection. Diagnosis of infection is by clinical history, and signs and symptoms of infection, along with supporting laboratory results, such as elevated white blood cell count on full blood count. Diagnostic investigations are done according to the clinical syndrome with which the patient presents.[22] Tests include culture of:
Blood
Sputum
Urine
Abscess fluid or debrided tissue
Aspirate from a joint suspected of infection
Tip of indwelling vascular catheter.
Infection with MRSA is established when cultures are positive. Additional tests such as echocardiography may be done to assess for possible endocarditis in patients with bacteraemia. Chest x-ray may be appropriate when a pulmonary infection is suspected. Polymerase chain reaction from fluid or tissue culture samples may be used to detect the mecA gene, confirming the presence of MRSA.[22]
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