Noah is an 18-month-old boy who has had a fever since yesterday evening. He’s been eating and drinking less than usual but wetting nappies regularly. He’s been miserable when hot but settles when his temperature comes down. His mum presented him to A&E because this morning, while febrile, he had an episode of shivering that lasted several minutes. He was conscious during the episode.
On examination, he has an erythematous pharynx with bilateral tonsillar enlargement and a runny nose.
You think he has a viral illness, but you have heard that rigors may be associated with an increased risk of bacterial infection?
What is a rigor?
A rigor can be defined as involuntary shaking or shivering associated with, “chills”, which is the sensation of feeling cold when febrile (Tokuda, 2005).
It occurs as a heat-gaining mechanism (muscle contraction), associated with behaviours brought with “chills,” such as seeking extra clothing or blankets, and other heat-retaining mechanisms, such as piloerection (“goose pimples”) (Ogoina, 2011).
Are rigors clinically significant?
In adult medicine, there seems to be an association with rigors and the risk of bacteraemia and invasive bacterial infections (Lee, 2012). This leads to the question about their significance in children, where fever is obviously a lot more common and the aetiology much more likely to be viral. After all, children are not just little adults.
Let’s take a look at the evidence…
There are two published studies looking at the risk of bacterial infection in children presenting with rigors.
One study was published from Israel in 1997 (Tal, 1997), which automatically should be interpreted with extreme caution. This was an era pre-HiB or Pneumococcal vaccines, which have transformed the landscape of invasive infections in children.
The study looked at children already admitted to the hospital due to infective aetiology and then compared the prevalence of confirmed or presumed bacterial infections in those who had rigors (67%) to those who did not have rigors (50%). They also compared the percentage of patients with positive microbiology who had rigors (15%) vs. those who did not (6%). The results are statistically significant. However, the clinical significance of rigors among this cohort of admitted patients is highly debatable.
A more recent case-control study, also from Israel, was published in 2017 (Erell, 2017), which more usefully examined children presenting to an emergency department with fever, with and without rigors.
Children with rigors were more likely to be older and have a higher temperature.
There was no difference in rates of serious bacterial infections between the two groups.
This study also needs to be interpreted with caution, as there were only 84 patients in each group, no cases of bacteraemia were reported, and the rates of SBI were high (~20% in each group). What is worth noting, however, is that the majority of children presenting with rigors did not have a bacterial infection.
So what about the NICE guidelines?
The NICE guidelines of “Fever in under 5s: assessment and initial management” (NICE, 2013), notes rigors as an “amber” sign, meaning children should be considered at intermediate risk of serious infection based on the presence of rigors. However, the evidence summary starts by saying,
“The evidence suggested that children with rigors were not more likely to have a bacterial illness than children who did not have rigors”.
Confused? Me too.
In summary, the group decided there wasn’t enough evidence to put it as a “red” feature, but since rigors seem to be associated with higher temperature, and a higher temperature is a risk factor for bacterial infection in itself…then rigors should be considered a risk factor. This is slightly confusing given that the evidence summary for height of temperature states that “on an individual basis, high temperature [is] not useful for detecting serious illness”.
So what does this all mean?
There is some low-quality and conflicting evidence suggesting a small increased risk of bacterial infection associated with the presence of rigours. However, this is perhaps because a rigor is a surrogate for a higher degree of fever. So, however you feel about the height of a temperature signifying an increased risk of bacterial infection, rigor is just a weaker reflection of this. It is worth remembering that SBIs are relatively rare, and rigors are relatively common; therefore most children who have an episode of rigor will still most likely have a viral illness.
Should the presence of a rigor be noted as part of your assessment? Yes.
Should it be a decisive factor? No.
Bottom line
Once age, the appearance of the child, and the presence or absence of a focus is taken into account, rigors add little to the assessment of the risk of bacterial infection in a febrile child.
Thanks for this helpful article- When I was a med student a general paediatric consultant listed for me the key diseases that would cause rigors (pyelonephritis, osteomyelitis, empyema and meningitis) and I still held this to be true until I read this.. I’m now Paeds ST6 and I’ve definitely been more likely to investigate kids when they present with rigors, also using the NICE traffic light system. I’ll continue assessing thoroughly but will no longer use rigors as such an important factor to change my decision to investigate in an otherwise well child.