Bacteriological conjunctival swab

A bacteriological conjunctival swab is a microbiological test that identifies from eye discharge the bacterium causing conjunctival inflammation (conjunctivitis) and tests which antibiotics it is sensitive to. Most bacterial conjunctivitis resolves on its own or with a short course of treatment, so a swab is taken when the inflammation is severe, recurrent or does not improve with treatment.

Who the test is intended for

• people with severe eye inflammation and abundant yellow or greenish purulent discharge;
• people with recurrent conjunctivitis;
• people whose inflammation lasts longer than expected;
• people whose inflammation does not improve with prescribed drops.

When to seek urgent ophthalmological care

Without waiting for a swab, see an ophthalmologist or emergency service if you have severe eye pain, blurred vision that does not clear with blinking or reduced vision, marked sensitivity to light, a red and painful eye while wearing contact lenses, an eye injury, a foreign body or chemical in the eye, or eyelid redness and swelling with a fever. A newborn with purulent eye discharge needs an urgent medical examination.

What a conjunctival swab is and what it shows

The conjunctiva is the thin mucous membrane covering the white of the eye and the inside of the eyelids. Bacteria are cultured in the laboratory from a sample collected with a sterile swab. The report lists the bacteria found and, if necessary, an antibiogram: a list of antibiotics to which the bacterium is sensitive or resistant. This helps the doctor choose effective drops or ointment.

Bacterial conjunctivitis usually begins with eye redness, yellow or greenish purulent discharge, eyelashes stuck together in the morning and burning or a gritty sensation in the eye, while vision remains normal. The inflammation often starts in one eye and spreads to the other. Watery discharge with a cold suggests viral inflammation, while intense itching in both eyes suggests allergy.

A bacteriological swab does not detect viruses, which commonly cause conjunctivitis, particularly with a cold, or allergic inflammation. Chlamydia, fungi and amoebae, which can endanger the eye in contact-lens wearers, require other tests selected by an ophthalmologist.

Preparation and swab collection

It is best to take the swab before starting treatment because an antibiotic can prevent bacterial growth and produce a false-negative result. Before swab collection, you need to be without eye drops and ointments containing an antibiotic or corticosteroid and without oral antibiotics for five days. Do not stop prescribed treatment on your own; discuss this with your doctor. On the day of the test, do not wash your eyes, apply drops or eye makeup, or wear contact lenses.

Collection takes a few seconds: the lower eyelid is gently pulled down and a sterile swab is passed along the inside. It is not painful, but may cause brief discomfort and watering.

How the report is interpreted

If no bacterium causing inflammation grows, or the report shows only normal eye bacteria, the inflammation is probably viral, allergic or caused by something this test does not detect. A positive result does not always mean that the particular bacterium is causing the symptoms, so the doctor interprets it alongside the examination and symptoms and decides on treatment based on the antibiogram.

How to arrange testing

A nurse takes the swab without an appointment or referral at all our branches (listed on the Contact). Prices for all tests are available in the service price list.

Frequently asked questions

Is taking an eye swab painful?

No. The swab only briefly touches the inside of the lower eyelid, so you may feel discomfort and your eye may water.

Does bacterial eye inflammation resolve on its own?

It usually resolves within five to seven days even without treatment. Clean discharge with cotton wool soaked in boiled and cooled water, using each piece only once. If the inflammation does not improve or worsens, see a doctor.

Can I wear contact lenses?

Not until the inflammation has resolved. Throw away disposable lenses worn during the inflammation. A red and painful eye while wearing lenses needs an urgent examination by an ophthalmologist.

Is conjunctivitis contagious?

Bacterial and viral inflammation spread by touch. Wash your hands frequently, avoid touching your eyes and use your own towel and pillowcase.