Introduction 

Enterobius vermicularis is more commonly known as pinworm, which is a common global intestinal nematode infection. Nematodes refer to a group of microscopic, tube-shaped organisms that can either be free-living or parasitic.¹ Transmission occurs when the microscopic eggs are ingested. Female worms deposit these eggs in the perinatal region during the night. These eggs might end up on hands, clothing and bedding. This makes person-to-person spreading highly efficient, especially in households or institutions such as schools or nurseries. The most common symptom is nocturnal perianal itching. However, around 30 to 40% of cases will present asymptomatically, making it harder to diagnose. This is because asymptomatic cases will evade clinical detection, which can lead to silent transmission, leading to an increased prevalence of the infection.²

Epidemiological overview 

Parasitic infections are one of the most common diseases, with enterobiasis being a common infection found in children. There is an estimated prevalence of enterobius infections in around 12.9% of children worldwide.³ However, this can range between 2.9% in Ethiopia to 17.2% in Iran. The World Health Organisation reports a range going as high as 28%. World Health Organisation (WHO).⁴ Roughly 200 million people are infected worldwide, with 30% of these cases being attributed to children aged five to ten years old.⁵ Children can act as reservoirs for the infection, causing household or institution-based spread. Ages 5 to 4 have the highest prevalence of infection rate. 

Challenges of asymptomatic carriers 

Around 30 to 40% of infections show no symptoms of infection, with one Polish study finding that 43.3% of children infected are asymptomatic.⁶ Silent transmission is concerning as it undermines normal hygiene routines and increases the risk of repeated infections. In an asymptomatic individual, there are no obvious warning signs of an infection, such as perinatal itching, to trigger a visit to a clinician or prompt families to reinforce stricter hygiene measures. The absence of symptoms can often lead to lapses in personal hygiene standards, such as improper handwashing after using the toilet or nail biting, which allows eggs to accumulate in the household. 

As pinworm eggs are highly resilient, they are capable of surviving on surfaces, including bedding, for up to two weeks.⁷ If surfaces are not cleaned properly, this can lead to the transference of eggs onto food or shared household items, causing indirect transmission. This results in reinfection cycles. Even if individuals are successfully treated, they can be reinfected by asymptomatic carriers in the same household or community. As these carriers are harder to identify, they act as a reservoir that can sustain transmission chains and delay eradication. In order to break this cycle, all individuals with the infection need to be treated, and hygiene education needs to be improved in order to ensure that any eggs are destroyed. 

Diagnosis

Clinical assessment is usually used to diagnose an infection, but asymptomatic individuals do not present with common symptoms such as perianal itching or sleep disturbance, meaning that clinical suspicion remains low. Stool exams can be used to detect infections, but are not commonly used. Faecal material only gives a positive diagnosis in 5 to 15% of infected subjects, as the pinworm eggs are not directly in the faeces. Adult pinworms are occasionally seen during a colonoscopy.⁸

The diagnostic standard is the perianal cellophane tape test. This is when a piece of tape is applied to the anal area in order to pick up deposited eggs. These eggs are then picked up via a microscope. In order to get an accurate diagnosis, the test must be done every morning for several days, as eggs are not laid every day, and the number of eggs differs.⁹

Public health challenges

As previously covered, asymptomatic carriers can lead to recurring infections, particularly in situations where many people are in proximity. It is often difficult to implement broad screening, as testing such as the tape test is intensive and requires early morning collection. This means that while it is useful to diagnose the individual, it is unsuitable for large-scale settings. There is also underreporting of infections due to the lack of symptoms. This can make it hard to estimate the true number of those infected and harder to allocate resources. 

Consequences of delayed treatment 

Whilst pinworm infections are often benign, in some cases they can lead to serious complications. Occasionally, the enterobiasis can migrate outside the intestines to ectopic sites such as the kidneys or lungs. This leads to intestinal perforation, which in turn can lead to bacterial peritonitis and to the patient turning septic.¹⁰ Pinworms have also been found in the fallopian tubes, which can cause fibrosis, which can affect fertility.¹¹ It is important to note that these cases are extremely rare; however, they highlight the importance of treatment. 

Summary 

Overall, asymptomatic enterobiasis is challenging to diagnose, as there is very little to raise clinical suspicion in the case of an infection. In addition, if asymptomatic enterobiasis is present in a community, such as a school or a home, this can act as a hidden reservoir leading to continual reinfection. 

FAQs

Can adults get pinworm if only children are symptomatic? 

Yes. Adults are often asymptomatic carriers and can reinfect children. 

Why doesn’t stool testing work for pinworm? 

Eggs are rarely present in stool. This means that a stool test might show a false negative. This means that a patient who is infected will appear uninfected. 

How long can pinworm eggs survive in the environment? 

Up to 3 weeks on bedding, clothing and surfaces 

Can pinworms go away without treatment? 

Unlikely. Infection persists through autoinfection and reinfection. Medication is the best way to remove the infection. 

Is pinworm dangerous? 

Usually mild, but in some cases, there can be significant complications.