The clinical course of herpes zoster: a prospective study in primary care

Authors: Helgason S, Sigurdsson J, Gudmundsson S.
Source: European Journal of General Practice. 2:12-16. March, 1996.
Institution: National University Hospital, Iceland.
Financial support: Icelandic Council of Science, Icelandic College of Family Physicians, Research Fund of the University of Iceland.

This paper was brought to my attention by one of its authors (Dr. Sigurdur Helgason). It is a nice illustration of an approach that is sure to become more widespread: the statistical analysis of data obtained via computerized medical records from a primary care setting.

Summary

Background

This study from Iceland was designed to obtain an accurate assessment of the incidence and course of herpes zoster in the primary care setting, making use of the increasing availability of computerized medical record systems in ambulatory practice.

Methods

Results Authors' Discussion

The authors compare their results to those of other studies, which have shown largely comparable findings. They note that their incidence of zoster in the younger population is higher than previously noted and that their incidence of post-herpetic neuralgia is similar to earlier studies but lower than that found in the placebo arm of recent trials of acyclovir. They estimate that a GP caring for 2000 patients can expect to see zoster four times a year and post-herpetic neuralgia lasting more than three months every other year, principally in the older population. Finally, in their series zoster was rarely associated with major illnesses.

Comment

This well-designed study provides detailed epidemiologic data about the incidence and course of herpes zoster, largely untreated with antivirals, in an outpatient, primary care setting. From a methodological standpoint, I have three caveats/questions. The authors present the sex and age distribution of patients with zoster in a graph, but this is not adjusted for the age distribution in the population studied and thus cannot be extrapolated to populations with different age distributions. Second, the authors do not specify exactly how the number of person years observed was obtained, which is central to the calculation of incidence. Was the number of person years observed calculated using patients actually in the medical records of the participating GP's, or was it based on patients in the geographic catchment area of these physicians? If the former, and if a significant number of people in the GP's catchment area were not in that physician's computerized records, the population at risk would have been underestimated and the incidence would have been overestimated. Finally, six-months follow-up time may be a bit short to conclude about the prevalence of malignancy in patients with zoster.

Beyond the data presented here, the concept of using outpatient computerized medical records to obtain data for such a study is an important one and raises a number of interesting issues:

5/9/96 

Reader comments

May 20, 1996
From: Sigurdur Helgason <sh@centrum.is>
The authors respond:
 
In answer to your questions.

First: I want to emphasize that the main reason and actually the only reason for this study was to find the point prevalence (traditionally called incidence in zoster studies of this kind) of postherpetic neuralgia at different time points after acute zoster in a primary care population. We have an age breakdown of 90% of the persons under observation, or a third of Icelanders. That is, nearly all practices could give the age distribution of the patients they cared for (registered). After comparing this with the age distribution of the total population (just over 261 thousand in 1992) we found it to be almost the same. We extrapolated from the 90% available, assuming the practices providing age strata were similar to those not providing this information.

Secondly: The number of person years was determined by multiplying the number of patients registered with each practice or GP by the duration of time each particular practice or GP participated in the study. Bias in estimating incidence due to a possible difference between catchment area/population and the population actually registered ("belonging") to a particular GP is not likely. The reason is that to be included as a case of zoster the patient had to be registered with a participating GP. All patients diagnosed with zoster but whose GP was not in the study were excluded, even if a GP in the study diagnosed them (during call or other services). This ment that GP´s not in the study, but who knew of it, often contacted me telling me about new cases in their care which I had to refuse, of course. One more point is that we kept a low profile with this study because we wanted only patients who normally would have sought medical attention for their zoster (avoiding publicity/referral bias).

Thirdly: I agree that 6 months is hardly enough follow up with malignancy in mind. What we did was to follow all for 12 months. I am a little obsessive when it comes to follow-up and those moving abroad were almost all eventually reached via phone. 99% follow-up over a year must be a record. The time frame of 6 months prior to or after the zoster episode was a collective decision. Actually, looking back at the data and extending this to 12 months after the zoster would not have changed the actual number of patients with malignancy "associated" with zoster.

Finally: Of the 14 patients still having pain after 12 months I have contacted eleven, 24 to 52 months after the zoster episode. One of the two patients with moderate pain was unchanged, but the other one defined his pain as mild and improving. Of the 12 patients with mild pain, two were worse, three better (pain free), four unchanged and three have not been reached/evaluated.

Sincerely,
Sigurður Helgason


Date: Sun, 04 Jan 1998
From: Intrade <intrade@worldnet.att.net>
Organization: Intrade

Sir,

In your study did you find any incidence of Herpes Zoster during pregnancy?
If so, how was it treated?
Did Herpes Zoster and/or its treatment lead to any birth defects?

Sincerely,

Manish H. Shah.
 

Dr. Sigurdur Helgason, study author, responds:

Date: Thu, 8 Jan 1998
From: Sigurdur Helgason <sh@centrum.is>

My short answer without going to the original data is:

Six women were known to be pregnant. None were treated and in no case were there any complications - maternal or foetal. At follow up (patient contact 12 months after the zoster and GP contact about 24 months after the zoster) there was no indication of complications. Although we should keep in mind that we did not examine babies or ask focused questions in that direction as it is our experience that zoster in pregnancy is a benign condition.

Sincerely yours Sigurður Helgason.



Date: Fri, 18 Sep 1998
From: BUNY2love@aol.com
 

I read with interest your perspective on clinical data bases in physician offices.  Conceptually this is where we all should be heading; however the US is still struggling with continuity of disease classifications at the hospital level.  So much of the classification process is geared toward reimbursement issues instead of clinical pertinence.  While it seems insurmountable to standardize coding, it's what is needed to control costs and improve patient care.

Sincerely
D. Jan Powell, MBA, RRA, CCS &
BS - Telecommunications Management
Health Information Services Consultant
 


November 12, 2000

Long term follow-up results of this study were published in the September 30, 2000 issue of the British Medical Journal, and are consistent with the results published in this paper.


 

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