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Sunday, November 30, 2008

Fever In A Newborn -- What to Expect When Your Infant Has A Temperature

A frequent reader of my blog may have noticed last week's post was published a day late. This was unfortunately due to our daughter spending the weekend in the hospital. Our daughter spiked a temperature of 101.1° F, which for a newborn requires a trip to the ER and a mandatory 48-hour hospital stay. In a way, I guess it is only fair that I should have to endure as a parent what I have inflicted on multiple mothers -- the ER work-up for a newborn with a fever. It was eye opening to be on the other side; although, I don't think I felt the same level of anxiety a typical mother feels when bringing her newborn to the hospital. Unlike most parents, I knew exactly what was going to happen. I knew the protocol for the work-up and the reasoning behind it.

Most parents probably think we, as pediatricians, are overly cautious when they call their on-call doctor because their newborn has a low-grade fever and are told to go to the ER. When they get there, they must be appalled by all the poking and prodding, the multiple cultures and the mandatory hospital stay by what can only seem like overzealous doctors.

But all this poking and prodding is the standard of care and it should be followed no matter what doctor or ER you bring your newborn, and for good reason. Any temperature of 100.5° F or greater in a newborn warrants a visit to the ER for a comprehensive work-up because a baby's immune system is not yet fully functioning. This is the reasoning behind not giving infants vaccines until they are 6-8 weeks of age and why new parents are encouraged to keep their newborns away from public places and sick relatives. Newborns cannot mount a mature immune response. In order to fight an infection, they depend on the antibodies that they received from their mothers' while in utero which will circulate in their bodies for a few months after birth. Breast-fed infants have the additional benefit of continuing to receive their mother's antibodies through her breast milk.

The only sign of a severe infection in a newborn may be a fever, increased irritability, poor feeding, or lethargy. For this reason, these symptoms are taken very seriously. The other concern is that newborns cannot compartmentalize infections very well. This means that an infection that starts in one place can quickly spread. Thus, the work-up for a fever is actually a work-up for sepsis (an overwhelming bacterial infection). There are three locations that must be checked for the bacteria -- the blood, the urine and the cerebral spinal fluid, CSF, which flows around the brain and down the spinal column. An infection of the CSF is called meningitis. Therefore all newborns with a fever need a blood culture, a spinal tap for a culture of the CSF and a catheterized urine culture. A urine culture collected with a bag instead of a catheter has a much higher rate of contamination and therefore can be more difficult to interpret. This could cause an infant to be diagnosed with a urinary tract infection when in fact there is none. When the blood culture and labs are drawn, an IV is placed so that the infant does not need to be stuck a second time in order to receive antibiotics.

In addition to the three cultures, a CBC (complete blood count) will be done in order to get an idea of how the infant's body is responding to the infection. The CBC may also help to predict whether the cause of the infection is more likely a virus or a bacteria. There are some preliminary tests that are done on the urine and CSF that are a good indication of whether or not there is an infection in either of these locations, but the definitive test is the culture. All three cultures are then watched in the lab to see if there is bacterial growth. It can take up to 48-hours for bacteria to grow. Until it is certain that there is no bacterial growth, the infant is treated with antibiotics. Thus, all newborns with a fever are admitted to the hospital for a minimum of 48-hours to receive IV antibiotics. If after 48-hours, there is no bacteria growth, the cultures are considered negative and it is conclude that the fever was due to a viral infection. Since antibiotics don't help with a viral infection, the antibiotics are stopped and the infant is sent home. If the cultures do grow bacteria, then the infant must stay in the hospital to receive a full course of antibiotics. This can be as long as two weeks.

When making that call to the pediatrician for a fever of 100.5° F, most parents don't expect that this will lead to a 48-hour hospital stay and multiple tests to ensure that the fever is not a symptom of a severe infection. But knowing what to expect takes a little of the fear out of the experience. And even though the work-up is mandatory, it is important to remember that most fevers in newborns are not caused by an overwhelming bacterial infection. Most infants will be just fine and will go home in 48-hours with no memories of the ordeal and with parents that are exhausted from the 2-day vigil.