**3. Agents**

**1. Introduction**

122 Advances in Common Eye Infections

need for surgical treatments.

**2. Epidemiological characteristics**

**2.1. Epidemiological significance**

regarding emerging diseases.

An infected eye is one of the major causes of corneal blindness after cataract in developing countries [1]. This is mainly induced by bacteria, fungi, yeast, and parasites. However, an increasing number of coinfections, which involve the presence of two or more pathogens, in the same place at the same time, affecting one or both eyes, are being reported. Comparing the single-microorganism infections, in which theoretically there is no competition, the coinfec‐ tions have been proven to have more mechanisms competing against the host resources. This competition is the main factor influencing the clinical course and evolution of the infection [2].

Eye coinfections represent a particular challenge for ophthalmologists; coinfections are difficult to diagnose because often the clinical picture is atypical and mimics different clinical pictures. In addition, eye coinfections respond poorly to antibiotics and usually present a slow clinical course. In these circumstances, it is common for patients to receive multiple treatments when they should be receiving a specific treatment; this can cause a refractory infection and

Although eye infections are common in immunocompetent patients, coinfection can compro‐ mise the immune system of the host [3, 4]. Therefore, the strategies used by each microorganism to survive against different treatments and the self-host immune response have important

This chapter provides a systematic review of the frequency and epidemiological characteris‐ tics, with reports of the most common clinical entities, produced by coinfection in the eye.

Ocular infectious processes are among the clinical entities that are relevant to the epidemiol‐ ogy. The high incidence of infections in patient care institutions has resulted in high-quality infection control processes and monitoring of various entities of epidemiological relevancy. For example, viral conjunctivitis primarily represents a challenge for management and prevention. Thus, it is common for diseases such as hemorrhagic conjunctivitis and follicular

The difficulty of the epidemiological surveillance of ophthalmic diseases lies in the limitation of performing a specific etiologic diagnosis of infection, since in practice ophthalmic infections are treated empirically based on the clinical picture and the physician's experience. Ophthal‐ mologists and laboratory staff should not forget that care of patients with endophthalmitis is usually performed at the first level of care, where the general practice is responsible for the greatest amount of attention to this disease. Thus, control programs for conditions such as trachoma are necessary to prevent them from reemerging and being attentive and vigilant

implications for the diagnosis and prognosis of the infection [5].

conjunctivitis to be part of the epidemiological surveillance.

Associated microorganisms may occur in different combinations. This association is predom‐ inantly bacteria-bacteria and to a lesser extent bacteria-fungus and bacteria-virus.

*Acanthamoeba* spp. and *Pseudomonas* spp. are associated because of their high resistance to empirical antibiotics and ulceration, which occurs primarily in association with *Acanthamoe‐ ba* spp., which is associated with *Legionella* spp., *Streptococcus* spp., herpes virus, *Moraxella* spp., *Candida* spp., etc.

Several viruses, bacteria, or fungi cause eye infections, but the pathogenic agent is modified extensively at presentation as a coinfection especially when the bacterium is coinfecting with different bacteria or a virus. In the case of fungi, when they are present with bacteria, only small changes are observed [3]. The clinical spectrum of keratitis can change when there is a coinfection between bacteria and *Candida* spp., mainly occurs; however, when endophthalmitis involves coinfection of a fungus and Gram-negative bacteria, the result is more unfavorable [6].
