Endogenous Bacterial Endophthalmitis
Endogenous bacterial endophthalmitis is caused by hematogenous dissemination of bacterial organisms, resulting in intraocular infection. This entity is uncommon and accounts for less than 10% of all forms of endophthalmitis. Patients who have compromised immune systems are most at risk for endogenous endophthalmitis. Predisposing conditions include diabetes mellitus, systemic malignancy, sickle cell anemia, systemic lupus erythematosus, and HIV infection. Extensive gastrointestinal surgery, endoscopy, dental procedures, and intravenous drug abuse may all increase the risk of endogenous endophthalmitis. Systemic immunomodulatory therapy and chemotherapy may also put patients at risk. Although the eye may be the only location where the infection can be found, there may be an extraocular focus in as many as 90% of cases. Possible sources of infection to be considered are tooth abscess, pneumonia, endocarditis, urinary tract infection, bacterial meningitis, and liver abscess. There may be a history of an indwelling line or port.
A wide variety of bacteria can cause endogenous endophthalmitis. The most common gram-positive organisms are Streptococcus species (endocarditis), Staphylococcus aureus (cutaneous infections), Bacillus species (from intravenous drug use), and Nocardia species (in immunocompromised patients; discussed in further detail in Chapter 10). The most common gram-negative organisms are Neisseria meningitidis, Haemophilus influenzae, and enteric organisms such as Escherichia coli and Klebsiella species. In Asia, infection from Klebsiella species in liver abscesses is the most common cause of endogenous endophthalmitis.
Clinical findings and symptoms
The clinical features of endogenous bacterial endophthalmitis are suggestive of an ongoing systemic infection and may include fever greater than 101.5°F, elevated peripheral leukocyte count, and positive bacterial cultures from extraocular sites (blood, urine, sputum). Patients may be ill and undergoing treatment for a primary underlying disease when they present with endogenous endophthalmitis. However, some patients may be ambulatory and afebrile. The underlying disease may include cancer treated with prolonged intravenous chemotherapy as well as other chronic infections, which may subsequently sequester in the eye. A nonocular infection serving as a nidus for bacterial dissemination to the eye may be very difficult to diagnose, especially in cases of osteomyelitis, sinusitis, or pneumonia misdiagnosed as a simple upper respiratory tract infection. In these situations, laboratory tests cannot substitute for a detailed history and review of systems.
Clinical symptoms include acute onset of pain, photophobia, and blurred vision. Examination usually reveals severely reduced visual acuity, and fibrin in the anterior chamber; hypopyon may be present; very rarely there may be periorbital and eyelid edema. There may be significant vitreous inflammation and vitreous cells. Sometimes, both eyes are affected simultaneously. Small microabscesses in the retina or choroid and white-centered retinal hemorrhages (Roth spots) may also be present.
Diagnosis is based on anterior chamber paracentesis and vitrectomy with vitreous and aqueous cultures and appropriate stains. As for cases of chronic postoperative endophthalmitis, PCR evaluation of ocular fluids with pan-bacterial or pan-fungal primers is extremely useful. Blood and other body fluid cultures should be used along with ocular culture results to confirm the diagnosis and establish therapy.
Intravitreal antibiotics are administered at the time of vitrectomy. If it is not clear whether fungal organisms may be involved, treatment of both fungal and bacterial etiologies is indicated at the time of vitrectomy. In addition, intravenous antibiotic treatment is sometimes required for several weeks, depending on the organism isolated. Similarly, in patients who have endogenous fungal endophthalmitis, systemic antifungal therapy may be warranted for 6 weeks or more. Initial antimicrobial choices may be empiric and subsequently tailored to culture results.
The complications of endogenous endophthalmitis can be serious. If the diagnosis of systemic infection is missed, the patient may develop sepsis and even die. In severe cases, recurrent or persistent intraocular infection may require numerous surgeries and repeat injections of intravitreal antibiotics. In addition, complications such as cataract development, retinal detachment, suprachoroidal hemorrhage, vitreous hemorrhage, macular scar, hypotony, and phthisis bulbi can occur in the most severe cases. The prognosis is directly related to the offending organism and the systemic status of the patient.
Excerpted from BCSC 2020-2021 series: Section 9 - Uveitis and Ocular Inflammation. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.