What is conjunctivitis? You probably know it as pink-eye, an unpleasant eye infection that you probably had once as a child. Conjunctivitis characteristically causes the eye and blood vessels, specifically the conjunctiva which is a clear membrane over the eye, to become inflamed causing the ‘pink’ appearance that earns it its name, as well as discharge from the eye.¹ Conjunctivitis can be caused by bacteria, viruses, fungi, and even parasites. However, the majority of infectious conjunctivitis cases are caused by adenoviruses. These are DNA viruses that carry their genetic material as DNA rather than RNA (DNA precursor) like a lot of other viruses.² They are quite difficult to get rid of even by cleaning, making them easily transmissible on surfaces or in the air, hence why children catch conjunctivitis this way, quite easily.³ 

Symptoms of adenoviral conjunctivitis

Adenoviral conjunctivitis, that caused by adenoviruses, causes the following symptoms in individuals:

• Sore throat (pharyngitis)
• Fever, usually considered to be 38°C or above
• Redness in the eyes 
• Watery or mucous discharge from the eyes
• Swollen lymph nodes
• Cough
• Runny nose
• Fatigue
• Headache
• Swollen, red tonsils
• Eye irritation or pain
• Sensitivity to light (photophobia)

Types of adenovirus and how it infects

There are a few types of adenovirus that can cause adenoviral conjunctivitis, for example in children, pharyngoconjunctival fever (pharyngitis and conjunctivitis) can be caused by human adenoviruses (HadV) 3, 4 and 7.³ There is a more extreme form of conjunctivitis called epidemic keratoconjunctivitis, which also affects the cornea as well as the conjunctiva and is caused by adenovirus serotypes 9, 18 and 37.⁴ 

But how exactly does adenoviruses cause a child to have conjunctivitis? Let's take the example of pharyngoconjunctival fever, as it is one of the more common types of conjunctivitis. For example, a healthy child may breathe in aerosol droplets produced when an ill child coughs or sneezes, meaning the adenovirus enters into the child’s airways.³ Once inside the body, the adenovirus binds to specific receptors on the surface of the respiratory epithelial cells,⁵ via the binder domain.⁵ This binding allows the virus to trigger the cell into engulfing it as a vesicle (endocytosis).⁵ To avoid being destroyed by the cell, the virus exits the vesicle and travels through the cell’s cytoplasm, jelly that fills cell, to the centre.⁵ The virus now moves towards the nucleus of the cell, an important cell component that houses the cell DNA, where it releases its own double-stranded DNA.⁵ Inside the nucleus, the adenovirus takes over the host cell's machinery to replicate its DNA and produce the building blocks for new viruses.⁵ These viral components are assembled into new virions, which are complete virus particles within the nucleus.⁵ As replication progresses, the cell's normal functions are disrupted, leading to cell damage and death.⁶

The newly formed virions are released when the host cell bursts (lyses), spreading the virus to neighbouring cells, and through the bloodstream to other parts of the body, most importantly the eyes.⁵ When the virus reaches the conjunctiva, the thin, semi-transparent layer covering the white part of the eye(sclera) and inner eyelids,⁴ it invades the cells triggering an immune response. The immune system recognises the adenovirus as foreign due to the antigens—specific proteins on the virus's surface that differ from the body's own proteins.⁵ These viral antigens activate immune cells to attack and destroy the infected cells, leading to the characteristic inflammation, redness, that is also called pink eye.⁵ The cycle of infection continues as these new virions can be shed in respiratory secretions, potentially spreading the virus to others.³

Vulnerability and modes of transmission of adenoviral conjunctivitis in children

Immature immune system in children

Children's immune systems are still developing and they may not have come into contact with certain serotypes of HadV. However, by the age of 5 a study showed that 70% to 80% of children surveyed had the corresponding antigen for HadV 3, 4 and 7.⁶ It has been suggested that children younger than 5 may have some maternal antibodies for their serotypes but it declines until they get infected themselves. Therefore, when they do become ill with conjunctivitis for the first time it may just be unavoidable due to their age and associated weak immune system.⁶

 Close contact in group environments (Schools, Daycare centres)

Children in schools, daycare centres, and other group settings are often in close physical proximity to one another.⁶ This close contact creates an ideal environment for the spread of adenoviruses through direct contact, respiratory droplets, or shared items, as younger children and infants are more likely to spend time indoors around each other without ventilation moving along the pathogenic aerosol droplets.⁶ The close quarters and frequent interactions among children make it easier for the virus to move from one child to another, contributing to outbreaks of conjunctivitis. Respiratory infections are also the most common type to be caused by adenoviruses in children,⁶ and respiratory infections in general are some of the most common infections spread between children.⁷ Additionally, approximately 7%-8% of respiratory infections in children are caused by HadV’s.⁶ 

Direct contact transmission

Adenoviruses can spread through direct contact with contaminated surfaces, such as toys, towels, or hands. A study into the survivability of HadV 19 (which causes epidemic keratoconjunctivitis) on office surfaces showed that the virus was detectable in a dried out form for up to 8 days on paper and up to 10 days on plastic, cloth and metal, which could all be communal surfaces children could touch.⁸ Moreover, children are more likely to touch their faces and eyes, which increases their chances of transferring the virus from a contaminated surface to the conjunctiva, leading to conjunctivitis.⁹ In communal environments, shared objects are often not cleaned thoroughly, which easily facilitate this type of transmission.⁹

Contaminated water (Swimming Pools)

Adenoviruses are resilient and can survive in poorly chlorinated swimming pool water, making swimming pools a common source of conjunctivitis outbreaks in children.¹⁰ An incident occurred in Sparti, Greece, in 1995, where a swimming event involving 238 young athletes led to an outbreak of adenoviral infections.¹¹ Shortly after the competition, people started to present symptoms like fever, conjunctivitis and a sore throat.¹¹ Investigations linked the outbreak to the pools insufficient chlorine levels, measured at just 0.2 mg/L—significantly below the level needed to effectively neutralize pathogens.¹¹ This incident underscores how critical proper chlorination is in preventing viral transmission in communal water settings.¹¹

A similar outbreak took place at a university in Beijing, China, where 55 individuals contracted adenoviral conjunctivitis after using a pool.¹² Tests confirmed that HAdV type 4 was present in both the patients and the pool water, suggesting that the virus had spread through contact with the contaminated water.¹² The transmission likely occurred through swallowing, inhaling, or eye contact with the water. The risk is amplified when an infected child enters the pool, as adenovirus can be shed into the water (even after the child has been ill), increasing the potential for spreading among other children.¹² Since children typically socialise closely in pools—playing, splashing, and frequently coming into contact with one another—this creates an ideal environment for the virus to spread.¹²

Poor hygiene practices

Young children often have poor hygiene habits, such as frequently rubbing their eyes, not washing their hands regularly, or sharing personal items like towels. These behaviours can facilitate the spread of adenoviruses, as the virus can easily transfer from hands to eyes, causing infection.¹³

The difference between adenoviral conjunctivitis and bacterial conjunctivitis

Bacterial conjunctivitis and adenoviral conjunctivitis (which includes pharyngoconjunctival fever, PCF) have different symptoms and treatments. Bacterial conjunctivitis usually causes thick, pus-like discharge and makes the eyes very red and swollen.⁴ The eyelids often stick together, especially after sleeping. It is treated with antibiotics. On the other hand, adenoviral conjunctivitis typically causes watery or mucous discharge and is often accompanied by a sore throat and fever.⁴ The eyes ]become red and slightly swollen, and in some cases, a thin, greyish film called a pseudomembrane can form on the inside of the eyelids.⁴ This film is not actually a true membrane but a layer of dead cells and mucus that can be scraped off. Adenoviral conjunctivitis is contagious, but antibiotics do not help with viral infections.⁴

How adenoviral diagnosis is confirmed

Laboratory diagnosis

For viral conjunctivitis, confirmatory tests like PCR (polymerase chain reaction) and viral cultures are highly accurate,¹⁴ allowing for the specific identification of the virus. PCR is particularly useful due to its rapid detection of viral DNA, while viral cultures, though slower, can provide a definitive diagnosis.¹⁵ 

Management of treatment and symptoms

Symptomatic treatment

The management of viral conjunctivitis focuses on symptom relief. Cool compresses and artificial tears are effective at reducing discomfort, such as burning, irritation, and redness.⁴ Antibiotics are not recommended for viral conjunctivitis, as they are ineffective and can contribute to antibiotic resistance. Instead, pain relief and maintaining moisture of the eye are important.⁴ 

Prevention of spread

Preventing the spread of viral conjunctivitis relies on good hygiene practices. Regular handwashing, avoiding touching the eyes, and not sharing personal items (e.g., towels, makeup) are critical steps.⁴ Children with viral conjunctivitis should stay home from school or daycare until their symptoms resolve to prevent outbreaks.⁴ Contaminated surfaces should be disinfected regularly to limit transmission.⁴

Complications and when to seek further medical care

Though viral conjunctivitis typically resolves without complications, keratitis—an infection of the cornea—can develop, particularly with more virulent strains like adenovirus.¹⁶ Signs of severe pain, photophobia, or vision changes warrant referral to an ophthalmologist.16 Early intervention can prevent permanent vision damage and ensure more specialised care when necessary.¹⁶

Summary

Adenoviral conjunctivitis, commonly known as pink eye, is a highly contagious eye infection often affecting children. It is caused by adenoviruses, which are resilient DNA viruses that can easily spread through respiratory droplets, direct contact with contaminated surfaces, or shared water in poorly chlorinated pools. Children are more vulnerable due to their developing immune systems and close contact in schools or daycare settings. Symptoms include red, watery eyes, sore throat, fever, and eye discomfort. While there is no cure, symptoms can be managed with supportive care like cool compresses and artificial tears. Proper hygiene, avoiding shared items, and staying home while infected can help prevent further spread. Early medical attention is advised if symptoms worsen or affect vision.