Tessa Davis. Do rigors indicate serious bacterial infection?, Don't Forget the Bubbles, 2013. Available at:
We often see children with pyrexia and have to decide on whether or not they have a serious underlying bacterial infection. When the parent describes, or uses the word ‘rigors’ we all get a bit twitchy ourselves. But is there any evidence to suggest that rigors = serious bacterial infection?
Some more background…
A chill is ‘a sensation of cold occurring in most fevers’.
A rigor is ‘a profound chill with pilo-erection associated with teeth chattering and severe shivering’.
There is general consensus that rigors indicate a rapid rise in temperature, but nobody seems to know whether it indicates bacteraemia.
What were the search terms?
Using PubMed, a search was run using
rigors OR rigor OR shaking
bacteraemia OR bacteremia OR sepsis OR septicaemia OR septicemia
How many studies have been carried out?
Unfortunately there is only one study on this topic – Tal et al (1997)
Lumsden and Potier reviewed this question for Emergency Medicine Journal in 2007 and also found only one result. There have been no new studies since then.
Ok, well I guess one will have to do. Who did they look at?
This was a prospective study which included:
100 patients who had a pyrexial illness (>38.5 degrees) along with rigors (febrile seizures were excluded)
334 patient who were matched in age, sex, temperature and clinical state but with NO rigors
What investigations did these patients have?
All patients had bloods (FBC, ESR, blood cultures); urine analysis and culture; and CXR. Some had lumbar punctures.
What was the outcome measured?
The outcome was presumed or proven bacterial infections.
Proven was from blood, urine or stool culture.
Presumed was from clinical assessment and CXR (the authors acknowledge that some of these may have been viral).
What were the results?
There were significantly greater positive blood cultures in patients with rigors (15%) compared to those without rigors (6%). This was more significant in those over 1 year old (p<0.015).
The most common pathogen was Strep pneumoniae.
In the presumed bacterial group, more patients had rigors. This was statistically signifianct (p<0.005)
How do we know what a rigor is?
Well, the short answer is….we don’t.
This study relied on parental reporting (60%) or health professional witnessing (40%).
There is nothing that clarifies the difference between a shiver and rigor so it does make selection a bit tricky.
Will/should this study change my practice?
It’s difficult to know what to take from this.
The recruitment of group is questionable as we really don’t know how accurate the assessment of having a rigor was (although that’s the same in actual practice).
That the outcomes include ‘presumed bacterial infection’ means that we don’t actually know whether or not there was a true bacterial infection in the ‘presumed bacterial group’. So the result that more patients in the presumed bacterial group had rigors is self-fulfilling and therefore not helpful to our practice.
Therefore, the useful outcome is that there was a significant different in positive blood cultures between the rigors and non-rigors group.
It is a small study and the definitions are sketchy, but it is something to go on.
I’m still confused – what’s the conclusion?
There has only been one study looking into whether rigors indicate an underlying bacterial infection. This study does show that more patients with rigors have a positive blood culture.
But the study was small, with definitional problems that have a huge impact on its usefulness.
Not one to hang your hat on, but bear it in mind when you see a patient with rigors.
Isselbacher KJ. Harrison’s principles of internal medicine, 13th ed. McGraw-Hill Inc. 1994, p83.