Why Repeat a Spinal Tap Before Stopping IV Acyclovir?

For babies with herpes simplex virus (HSV) that involves the central nervous system (CNS disease), doctors usually recommend a second spinal tap near the end of the intravenous (IV) treatment. The goal is not to prove that the virus is completely gone from the entire body, but to check whether HSV DNA is still detectable in the fluid around the brain and spinal cord ^[1]. If the virus’s DNA is still found, the IV treatment must continue to protect your baby’s developing brain ^[2].

The 21-Day Minimum Course and Why We Retest

When a newborn has CNS HSV disease, the standard treatment is a minimum 21-day course of high-dose intravenous (IV) acyclovir ^{[2] [3]}. However, day 21 is a milestone, not an automatic stopping point ^{[1] [2]}.

To safely decide if the IV medication can be stopped, the medical team performs a repeat lumbar puncture (spinal tap) to collect cerebrospinal fluid (CSF)—the fluid that surrounds and protects the brain and spinal cord. They run a highly sensitive PCR test on this fluid to look for any remaining viral DNA ^[1].

What to expect during the procedure: During a lumbar puncture, the baby is carefully positioned, and a small needle is placed in the lower back, below where the spinal cord ends. The medical team will use pain control and comfort measures to keep your baby as calm as possible. While no procedure is completely without risk, it is a routine test done to ensure your baby’s safety.

What Happens if the Test is Positive?

If the repeat PCR test still detects HSV DNA in the spinal fluid, it means the infection is not fully controlled yet. In this case, doctors will extend the IV acyclovir treatment rather than stopping it ^{[1] [2]}.

Stopping the IV medication while the virus is still active in the central nervous system is dangerous, as ongoing viral inflammation can lead to severe complications such as seizures or permanent brain injury ^{[4] [5]}. The repeat test is used precisely to prevent this by identifying persistent infection so treatment can continue. If the IV treatment is extended, the medical team will typically repeat the spinal tap again (often in about a week, based on your hospital’s protocol) until the result is negative ^{[1] [3]}.

What Happens After a Negative Result?

A negative PCR result is an encouraging milestone. It means HSV DNA is no longer detectable in the spinal fluid, which is a key factor the medical team uses to decide that it is safe to stop the IV treatments ^[6].

However, a negative test does not mean the virus is permanently eradicated from the body, as HSV can hide silently in nerve cells and potentially reactivate ^[6]. Because of this risk, your baby will likely transition to an oral antiviral medicine (liquid acyclovir) to take at home for 6 months ^{[7] [1]}.

This “suppressive therapy” is often given multiple times a day, and the dose will be adjusted as your baby grows. Studies show that this 6-month treatment helps improve long-term neurodevelopmental outcomes and reduces the chances of skin recurrences, though it cannot guarantee normal development ^{[7] [1]}. During this time, your baby will need follow-up appointments to monitor their development, hearing, kidney function, and blood counts (as the medication can sometimes lower white blood cell counts).

Watching for Signs of Recurrence

Even with oral suppressive medication, it is important to monitor your baby closely after discharge. Do not wait for a scheduled appointment if you are concerned. Contact the treating team urgently or seek emergency care if your baby experiences:

• A fever
• New blisters or skin lesions
• Unusual sleepiness or marked irritability
• Poor feeding
• Seizures or sudden neurologic changes
• Breathing difficulty
• Eye redness