RSV primer: testing

I start checking the CDC site daily for RSV updates around mind-October. To some that may be paranoid, but Oliver has suffered through two major hospitalizations with RSV, so I figure forewarned is the first step in being forearmed. For most 7-year-olds RSV is a cold, typically a really snotty nose. Not to preemies, whose tiny airways and often damaged airways fill with secretions and go into spasm. RSV is also the 2nd most common type of viral pneumonia (infection of the lung tissue). RSV is especially dangerous for preemies with bronchopulmonary dysplasia (BPD, structural changes and inflammation of the lung due to prematurity). Both my boys have that, but Oliver also has congenital heart disease, which makes him even more vulnerable. In 2006 when the boys were 2 1/2 they had RSV (first winter off Synagis). Victor, who actually has worse lungs, was sick at home for 4 days needing nebulizers round the clock for about a day. Oliver spent 7 days in the intensive care unit leading me to believe that heart problems are as bad or even worse than BPD. Oliver was also hospitalized for 5 days with RSV when he was 6, basically unheard of. So let’s just say I am RSV paranoid. RSV is also very dangerous for the elderly, people in nursing homes, and anyone with a suppressed immune system.

As there is a little blip in the CDC’s RSV tracker, it seems it is that time of year again. So, if your preemie is sick getting tested for RSV is probably a good idea. Why? Because it will help you know how sick your child might be. Even if they are lucky and don’t need to be in the hospital, you’ll know to keep a much closer eye on things for the next few days because they are likely to be sick longer than they would be with a common coldIn addition, any sign they are not improving or getting worse should not be taken lightly.

For example, last year Oliver got sick on a Friday. We were seen Saturday am and told “probably a virus.” No RSV testing was done (or pertussis, but that was before the big outbreak, so I’m ok with that). “Give him nebs, keep a close eye on him,” yada, yada yada. Saturday night he gets worse, so off we go to the ER. He has a fever of 104, no clear pneumonia on chest x-ray, but because he is so sick antibiotics are started. He needs nebulizers every hour.He is swabbed for RSV sometime Sunday night and Tuesday am the test comes back positive. Now that there is an explanation for his fever and lung crud, his antibiotics can be stopped and the RTs start pounding on his chest to bring up all that lovely RSV gunk.

The point? If he was tested on Saturday morning we would have known that information at least a day earlier, and his care could have been optimized sooner (later this week I’ll blog about optimal care for RSV). Knowing he has RSV also helps the doctors decide how long he should be sick, so if he doesn’t improve when expected they can look for other things. Having as much information, whether the results are positive or negative, is really important for children (and adults) with complex illness.

So what tests should you ask for? They are all swabs taken deep from the nose and there are three:

A PCR test. This test looks for fragment’s of the RSV genetic material. It is the most sensitive, meaning it is less likely to miss RSV. Ask for this test, because preemies get sicker with less virus. For example, say it takes 1000 RSV viruses to get sick for an average 2 year old, a preemie with BPD who is 2-years-old might only need 400 particles to get sick, and a preemie with BPD and heart disease might only need  200 viral particles. The PCR test is more likely to pick up that child who is sick but has fewer viral particles (doctors call this the viral load). The PCR is so sensitive because the sample is treated in such a way that the genetic fragments are multiplied millions of times before testing. With PCR you literally only need one tiny fragment of genetic material to have a positive test.

Another test is a culture, actually growing the virus in a lab. This is a fairly good test, but more labor intensive and has a longer turnaround than a PCR. The PCR will also pick up more positives than a culture.

The third test is an antigen test and is the gold standard a lot of places. An antigen test looks for a piece of the surface of the virus (antigens are found on the surface of cells). Unlike PCR, there is no amplification, so an RSV antigen test is only positive 80-90% of the time. Meaning on a good day 10-20% of cases are missed. As preemies can get sick with less virus, they are more likely to fall in this “missed diagnosis” category.

Bottom line? My recommendation is the PCR test hands down. Preemie lungs are not the same. If you doctor gives you grief, tell them to read this post! A preemie is more likely to get really sick with less virus.

What if the PCR just isn’t available? Your hospital lab may simply not do the PCR, or your insurance may not cover it. In that case the next best choice is an antigen test (it’s faster), but insist on a culture as well as back up (this is done all the time), so if the antigen test is negative, you will have another shot at picking up any missed virus.

If I didn’t make that clear please post questions in the response section. Molecular diagnostics can sometimes come across as a bad game on mental Twister!

Remember, this post is not direct medical advice, just my opinion.

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4 Responses to RSV primer: testing

  1. Melissa says:

    Thank you! This is so helpful. My daughter was approved for Synagis this year (her second winter) from October through March, and we are in NY. I am thrilled, even with the high co-pay it is worth it.

  2. Kara says:

    Hi, I have the book Preemie Primer and have found it invaluable, thank you! On pg 226, RE: RSV and the Synagis vaccine it mentions that there is information about working out insurance hassels, filing appeals, and the patience assistance program on this website- but I can’t find anything. Can someone direct me to where I may find that? Thanks so much!

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