Abstract

Eye and blood infections represent a significant health concern globally, posing challenges in diagnosis and management. This abstract provides a comprehensive overview of the clinical presentation and diagnostic approaches for these infections. Eye infections, including conjunctivitis, keratitis, and endophthalmitis, manifest with symptoms such as redness, discharge, pain, and vision changes. Timely diagnosis is crucial to prevent complications like vision loss and systemic spread. Diagnostic modalities range from clinical examination to laboratory tests, including culture, PCR, and imaging techniques like optical coherence tomography (OCT) and ultrasound. Bloodstream infections, commonly caused by bacteria, fungi, or viruses.

Keywords: Keratitis, Eye infection, Blood infection,  Bacteremia,  Septicemia

Introduction

Eye Infections

Clinical Presentation

Infectious agents may become introduced to any part of the eye, either externally or from an endogenous source. External infections usually involve the superficial structures—the conjunctiva and the cornea—unless there has been a penetrating injury that introduces microbes into the globe. Endogenous infections frequently occur when microorganisms present in the blood, such as those causing endocarditis, enter the eye. They can also arise from the reactivation of dormant viruses or parasites, such as CMV or toxoplasmosis (Leibowitz, 2000).

Structural Biology

Conjunctivitis and Keratitis

The conjunctiva is a thin membrane that covers the eyelid (palpebral conjunctiva) and reflects onto the outer surface of the eyeball, the sclera (bulbar conjunctiva). The central cornea is not covered. The conjunctiva may be infected by a variety of many microbes, most of which inhabit the upper respiratory tract. The exudates in bacterial infection are particularly thick, sticky and encrusted, so the eyelids may stick together. Acute noninfectious inflammation may also develop in patients with seasonal allergies. Conjunctivitis is extremely contagious; the illness can be easily transmitted to the opposite eye or to other individuals through direct contact, such as touching the infected eye and subsequently the healthy eye (Syed & Hyndiuk, 1992).

Keratitis, which is the inflammation of the cornea, is a significantly more severe illness compared to conjunctivitis. Unlike the brief pain caused by conjunctivitis, keratitis can lead to permanent damage and blindness.  The aetiology of this phenomenon can be attributed to infectious organisms across all categories. S. aureus is the predominant bacterial agent (Liesegang, 1992). Filamentous moulds, particularly Fusarium spp. and Aspergillus spp., as well as yeast, namely Candida spp., can cause a lesion that may appear similar to a bacterial infection. This similarity might lead to a delay in diagnosing and treating the condition effectively (Klotz et al., 2000). The herpes simplex virus can lead to the development of a kind of ulcerative lesion known as dendritic keratitis, characterised by its branching pattern (Mader & Stulting, 1992). Shingles, caused by the reactivated varicella-zoster virus, can lead to a type of eye inflammation called keratitis if it affects the ocular branch of the trigeminal nerve (also known as the fifth cranial nerve) (Starr & Pavan-Langston, 2002). Acanthamoeba spp., a type of free-living amoeba, can cause painful ulcerative lesions in individuals who wear contact lenses (Ma et al., 1990). These lesions can be rather uncomfortable. Interstitial keratitis, produced when blood vessels grow into the cornea from the conjunctiva, is the most common cause of blindness in the world. Trachoma is a form of chronic keratoconjunctivitis that is produced by C. trachomatis (Jones & Batteiger, 2000). The scarring that can result from recurrent disease has six million people worldwide. The World Trachoma Initiative aims to eliminate this treatable infection by 2020. In parts of Africa, a filarial parasite, Onchocerca volvulus, which is transmitted by black flies (Simulium spp.), produces an intense inflammatory response when migrating worms die, resulting in river blindness (Hall & Pearlman, 1999). Other causes of interstitial keratitis include T. pallidum (syphilis), Mycobacterium leprae (leprosy), and M. tuberculosis (tuberculosis). Keratitis (and blindness) can also be produced by noninfectious injury, such as trauma, ultraviolet radiation (i.e., the reason for not looking directly at the sun, particularly during an eclipse) and conditions that diminish the tears that lubricate the cornea.

Uveitis and Endophthalmitis

The most serious infections are those that affect the interior of the eye. Endogenous infections reach the eye through the bloodstream. A variety of bacteria, fungi, and viruses may be responsible. Likely the most common cause is endocarditis, wherein the eyes, as well as various other organs, are seeded by the continuous bacteremia. Other endogenous infections include reactivation of latent viruses and parasites, such as cytomegalovirus and T. gondii, respectively. Exogenous infections are usually associated with penetrating trauma to the eye. A special category is postsurgical infection. An exogenous parasitic source is the infection with animal helminthic parasites, such as Toxocara canis, T. cati, or Baylisascaris. The infection of humans by these parasites results in visceral larva migrans, wherein the immature larvae wander since they are in the wrong host; these infections commonly involve the eyes and the CNS (Sandhu et al., 2019).

Diagnosis of Eye Infections

Collection of Specimens

Conjunctivitis is usually diagnosed with a swab of the affected conjunctiva, which can be placed in an appropriate transport medium. All other infections are appropriately collected by an ophthalmologist. Keratitis is addressed by scrapings of the affected lesion; if a bacterial or fungal etiology is suspected, material is often inoculated directly onto appropriate media by the clinician. Specimens for the diagnosis of endophthalmitis must be collected surgically.

Microscopic Examination

Depending on the pathogen suspected and quantity of specimen, Gram’s stain, calcofluor white or Wright’s stain (or equivalent) should be performed. If tissue is obtained surgically, appropriate stains for infectious agents should be done.

Culture

The appropriate media to inoculate depends on the clinical assessment of the most likely etiologies. Most of the commonly encountered bacterial and fungal pathogens can be cultivated on routine media. For certain pathogens, such as the agents of syphilis, leprosy, and parasitic infection, the diagnosis must be made microscopically or serologically.

Blood Infections

Clinical Presentation and Pathogenesis

Bacteremia and Septicemia

The suffix “-emia” pertains to the cardiovascular system. Bacteremia, fungemia, and viremia are conditions characterised by the presence of bacteria, fungus, and viruses, respectively, circulating inside the circulatory system. Signs and symptoms may be present, however they are not always consistent. If the patient lacks awareness of the illness, specifically the presence of circulating microorganisms, the condition is referred to be “silent” or “subclinical.” Septicemia, often known as sepsis, is a medical condition that presents with symptoms such as fever, chills, general discomfort, rapid heartbeat, increased breathing rate, and signs of toxicity or extreme weakness. Septicemia occurs when bacteria in the bloodstream multiply faster than they can be eliminated by phagocytes. The symptoms are caused by microbial poisons and/or cytokines released by inflammatory cells (Parrillo, 1993). It is now evident that the activation of cytokines leads to a sequence of significant immunosuppressive occurrences. Organ failure is a critical aspect of sepsis that can result in death, however the specific pathways that cause this outcome are not well understood. Sepsis is traditionally associated with gram-negative bacteria, which contain endotoxin. It is now well appreciated, however, that gram-positive bacteria and fungi can also cause the sepsis syndrome (Aube et al., 1992).

Types of Bacteremia

Bacteremia can be temporary, sporadic, or persistent, indicating many ways that bacteria might enter the bloodstream. When microorganisms, frequently from the normal microbiota, enter the bloodstream by minor membrane damage (such as brushing one’s teeth, straining during bowel motions, or medical operations), transient bacteremia results. Periodically, bacteria from an infected site are released into the bloodstream through extravascular abscesses, causing intermittent bacteremia. This can lead to the spread of cellulitis or infections of bodily cavities, including empyema, peritonitis, or septic arthritis. When an infection is intravascular, as in the case of bacterial endocarditis or aneurysms, or when it is embedded in hardware, such as arteriovenous fistulas, intra-arterial catheters, or indwelling cannulas, continuous bacteremia typically results. However, in as many as one-third of cases of bacteremia, the origin of the organisms may not be identified.

Secondary bacteremia can arise from an infection within a tissue or organ. Nonetheless, the original site (primary bacteremia) is frequently invisible. It is plausible that the host defence mechanisms in this case failed to effectively eradicate a brief case of bacteremia. It has been demonstrated that colonising bacteria in the nose, at least in the instance of S. aureus, may be the cause of the systemic illness. (von Eiff et al., 2001). The factors that trigger dissemination from the anterior nares remain unclear, but simple mechanical spread to the skin and subsequent infection of wounds or intravascular devices is one possibility. When an infection in an organ spills over into the blood (Musher et al., 2000). Conversely, bacteremia can result in disseminated infection in distant organisms, a phenomenon that is termed“metastatic infection.”

Another way to categorise bacteremia is as nosocomial or community-acquired. Both immunocompetent and immunosuppressed hosts may experience it. Depending on these variables, together with the patient’s age, the kinds of organisms and the prognosis of the ensuing infection differ significantly (Siegman-Igra et al., 2002).

Both gram-positive and gram-negative bacteria have been found in the bloodstream (Diekema et al., 1999). The nature of the infectious microbiota has clearly changed during the last few decades. Over that period, the number of yeast isolates and clinically relevant coagulase-negative staphylococci has grown while the number of anaerobic isolates has dropped. Bacteremias caused by non-fermenting gram-negative bacilli are more likely to be polyclonal, or to have many molecular types, than bacteremias caused by other gram-negative bacilli, for unknown reasons. This field has probably been impacted by modifications to intravascular access line utilisation and pre-surgical prophylaxis procedures.

Some microorganisms have distinct clinical implications. Clostridium septicum is usually related with neoplastic illness, notably colon cancer, and can cause distant metastatic abscesses. Similarly, bacteremic Streptococcus bovis is frequently related with endocarditis and colonic diseases, including colon cancer. Rarely, episodes of C. perfringens bacteremia generate sudden, dramatic hemolysis, which can be deadly; the hemolysis is caused by clostridial toxins, but it is unclear why the fatal hemolysis occurs in such a small fraction of clostridial bacteremia cases.

Blood Cultures Collection

According to Reimer et al. (1997), laboratory directors are responsible for making decisions regarding a list of critical factors. These factors include the type of collection, the number of blood cultures, the timing of those blood cultures, the volume of blood that is to be cultured, the amount of culture medium, the composition of the culture medium, when and how frequently to subculture, and the interpretation of the results.

It is imperative to implement all necessary measures to reduce the proportion of tainted blood cultures. Although they can also cause diseases connected to lines, isolates of Corynebacterium spp., P. acnes, and Bacillus spp. other than B. anthracis are typically considered contaminants. The majority of β-hemolytic streptococci, yeast, gram-negative bacilli, Enterococcus species, Streptococcus pneumoniae, and Staphylococcus aureus isolates have clinical significance. Coagulase-negative staphylococci are the most problematic isolates because, despite being the primary cause of genuine bacteremia, they are also part of the skin’s natural microbiota (Weinstein, 2003).

Regular monitoring of contaminated samples should be conducted in all microbiology laboratories to provide quality assurance. The acceptable contamination rate for blood cultures is less than 3%. According to Bates and associates, a contaminated blood culture can result in a patient’s hospital bill increasing by 20% to 39% due to a longer stay for intravenous antibiotic medication and extra testing (Waltzman & Harper, 2001).

Additionally, they highlighted the need of utilising paired blood culture sets to identify potential contamination when only one set yields a positive result. If the collecting procedure is effective and contamination is minimised, the cost of impurities becomes tolerable. To discourage inappropriate antibiotic use, a laboratory strategy can be implemented that does not regularly test single isolates of coagulase-negative staphylococci for antimicrobial susceptibility (Aiesh et al., 2023).

Culture Media

The media utilised in blood culture bottles are versatile and nutritionally fortified. Commonly employed options include tryptic or trypticase soy, supplemented peptone, brain-heart infusion, Columbia CNA agar, and Brucella broths. All of these products are readily accessible for purchase. However, differences in the composition of the same type of media produced by various producers make it challenging to evaluate and draw conclusions about the relative amounts of bacteria obtained from each.

Typically, blood culture media that may be purchased commercially contain the anticoagulant SPS at concentrations that range from 0.025% to 0.05%.

 In addition to anticoagulant properties, SPS also inactivates neutrophils and certain antibiotics, including streptomycin, kanamycin, gentamicin, and polymyxin, and precipitates fibrinogen, β-lipoproteins, βCglobulin, and other components of serum complement. SPS may also inhibit the growth of certain bacteria—Peptostreptococcus anaerobius, N. gonorrhoeae, and N. meningitidis. The inhibitory effect of SPS can be neutralized by adding gelatin to the medium, to a final concentration of 1%.

Many current blood culture bottles incorporate synthetic antibiotic-removing resins. Recovery of pathogens, and, unfortunately also skin contaminants, is clearly improved by these additions (Weinstein, 2003). In a study of paired blood cultures, the use of resin media significantly improved the recovery of members of the family Enterobacteriaceae, Enterococcus spp., S. pneumoniae and viridans streptococci (Bale & Murph, 1997).

Traditionally, blood culture sets consisted of a bottle designed to recover aerobic bacteria and one engineered for anaerobic bacteria. In actuality, the majority of all types of bacteria are recovered in both bottles. The change in the pattern of bacteremia’s over time described above has led some investigators to suggest that an “anaerobic” bottle be limited to situations in which anaerobes might be expected (e.g., in patients with abdominal disease processes). Recovery rates from three different paired bottle systems were compared: (1) one aerobic and one anaerobic bottle (5 mL of blood each); (2) two aerobic bottles (5 mL each); and (3) two aerobic bottles plus an extra anaerobic bottle when anaerobic infection was clinically suspected. The third approach had the largest yield of isolates. From their data, these investigators concluded that the use of two aerobic bottles with selective culturing for anaerobes will potentially increase the number of clinically important isolates by at least 6% (Morris et al., 1993). The policy of substituting a second “aerobic” bottle for the “anaerobic” bottle is not a common practice, probably in part because of the difficulty of deciding which patients would benefit from the practice and the impossibility of leaving the decision to the clinical staff.

Another reason is likely that others have demonstrated that anaerobic bacteremia’s are not predictable, so an anaerobic bottle should be included in every blood culture set. It has been shown that many facultative anaerobic bacteria (the majority of human pathogens) grow well in the “anaerobic” bottle (Clarridge et al., 2001). It should be noted that the policy at one institution, where a decreasing incidence of anaerobic bacteremia’s had also been documented, included two aerobic components in addition to the nonvented “anaerobic” bottle.

Conclusions

Diagnosis of eye infections often involves a thorough physical examination of the eye, including visual acuity testing and examination of the anterior and posterior segments. Additional diagnostic tests such as cultures, swabs, and imaging techniques like optical coherence tomography (OCT) or ultrasound may be utilized to identify the causative organism and assess the extent of the infection. For blood infections, also known as bloodstream infections or sepsis, clinical presentation can vary widely but may include fever, chills, rapid heartbeat, rapid breathing, low blood pressure, and altered mental status. The symptoms can be nonspecific, making diagnosis challenging. Diagnosing blood infections typically involves blood cultures to identify the causative microorganism. Other laboratory tests, such as complete blood count (CBC) and inflammatory markers like C-reactive protein (CRP) and procalcitonin, may also aid in diagnosis and assessing the severity of the infection.

In both cases, prompt and accurate diagnosis is essential for initiating appropriate treatment, which may include antimicrobial therapy, antifungal agents, antiviral medications, or other targeted interventions. Collaboration between ophthalmologists, infectious disease specialists, and other healthcare professionals is often necessary for comprehensive management and optimal patient outcomes.

Acknowledgment

None .

Conflicts of Interest

None.

References

• Aiesh, B. M., Daraghmeh, D., Abu-Shamleh, N., Joudallah, A., Sabateen, A., & Al Ramahi, R. (2023). Blood culture contamination in a tertiary care hospital: a retrospective three-year study. BMC Infectious Diseases, 23(1), 448.
• Aube, H., Milan, C., & Blettery, B. (1992). Risk factors for septic shock in the early management of bacteremia. The American journal of medicine, 93(3), 283-288.
• Bale, J. F., & Murph, J. R. (1997). Infections of the central nervous system in the newborn. Clinics in perinatology, 24(4), 787-806.
• Clarridge III, J. E., Attorri, S., Musher, D. M., Hebert, J., & Dunbar, S. (2001). Streptococcus intermedius, Streptococcus constellatus, and Streptococcus anginosus (“Streptococcus milleri group”) are of different clinical importance and are not equally associated with abscess. Clinical infectious diseases, 32(10), 1511-1515.
• Diekema, D. J., Pfaller, M. A., Jones, R. N., Doern, G. V., Winokur, P. L., Gales, A. C., … & SENTRY Participants Group (Americas). (1999). Survey of bloodstream infections due to gram-negative bacilli: frequency of occurrence and antimicrobial susceptibility of isolates collected in the United States, Canada, and Latin America for the SENTRY Antimicrobial Surveillance Program, 1997. Clinical Infectious Diseases, 29(3), 595-607.
• Hall, L. R., & Pearlman, E. (1999). Pathogenesis of onchocercal keratitis (river blindness). Clinical Microbiology Reviews, 12(3), 445-453.
• Jones RB, Batteiger BE. Chlamydia trachomatis (trachoma, perinatal infections, lymphogranuloma venereum, and other genital infections). In Mandell GL, Bennett JE, Dolin R, Eds. Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases. 5th Ed. Philadelphia, PA: Churchill Livingstone, 2000:1989–2004.
• Klotz, S. A., Penn, C. C., Negvesky, G. J., & Butrus, S. I. (2000). Fungal and parasitic infections of the eye. Clinical microbiology reviews, 13(4), 662-685.
• Leibowitz, H. M. (2000). The red eye. New England Journal of Medicine, 343(5), 345-351.
• Liesegang, T. J. (1992). Bacterial keratitis. Infectious Disease Clinics of North America, 6(4), 815-829.
• Ma, P., Visvesvara, G. S., Martinez, A. J., Theodore, F. H., Daggett, P. M., & Sawyer, T. K. (1990). Naegleria and Acanthamoeba infections. Clinical Infectious Diseases, 12(3), 490-513.
• Mader, T. H., & Stulting, R. D. (1992). Viral keratitis. Infectious Disease Clinics of North America, 6(4), 831-849.
• Morris, A. J., Wilson, M. L., Mirrett, S., & Reller, L. B. (1993). Rationale for selective use of anaerobic blood cultures. Journal of Clinical Microbiology, 31(8), 2110-2113.
• Musher, D. M., Alexandraki, I., Graviss, E. A., Yanbeiy, N., Eid, A., Inderias, L. A., … & Solomon, E. (2000). Bacteremic and nonbacteremic pneumococcal pneumonia a prospective study. Medicine, 79(4), 210-221.
• Parrillo, J. E. (1993). Pathogenetic mechanisms of septic shock. New England Journal of Medicine, 328(20), 1471-1477.
• Reimer, L. G., Wilson, M. L., & Weinstein, M. P. (1997). Update on detection of bacteremia and fungemia. Clinical microbiology reviews, 10(3), 444-465.
• Sandhu, H. S., Hajrasouliha, A., Kaplan, H. J., & Wang, W. (2019). Diagnostic utility of quantitative polymerase chain reaction versus culture in endophthalmitis and uveitis. Ocular Immunology and Inflammation, 27(4), 578-582.
• Yardena, S. I., Boaz, F., Ruth, O. W., Yoav, G., Aliza, N., David, S., & Michael, G. (2002). Reappraisal of community-acquired bacteremia: a proposal of a new classification for the spectrum of acquisition of bacteremia. Clinical infectious diseases, 34(11), 1431-1439.
• Starr, C. E., & Pavan-Langston, D. (2002). Varicella-zoster virus: mechanisms of pathogenicity and corneal disease. Ophthalmology clinics of North America, 15(1), 7-15.
• Syed, N. A., & Hyndiuk, R. A. (1992). Infectious conjunctivitis. Infectious disease clinics of North America, 6(4), 789-805.
• Von Eiff, C., Becker, K., Machka, K., Stammer, H., & Peters, G. (2001). Nasal carriage as a source of Staphylococcus aureus bacteremia. New England Journal of Medicine, 344(1), 11-16.
• Waltzman, M. L., & Harper, M. (2001). Financial and clinical impact of false-positive blood culture results. Clinical infectious diseases, 33(3), 296-299.
• Weinstein, M. P. (2003). Blood culture contamination: persisting problems and partial progress. Journal of clinical microbiology, 41(6), 2275-2278.