Background

Urolithiasis is a common condition. About one in eight men and one in twenty women will develop a stone within their lifetime. Recurrence rates are high and those who form calculi have a 10% recurrence rate at 1-year 1. Urolithiasis affects people in the prime of life and in addition to causing pain and suffering; it causes a loss of productivity with time away from work. In western societies urolithiasis accounts for 16% of all urological admissions and 1-2% of total hospital admissions 2.

A number of important risk factors pertaining to urolithiasis include age, sex, diet, water intake; body weight and past history have been well documented3. The effect of season and geographical location is however equivocal. Several studies of urolithiasis in Emergency Departments in the Northern Hemisphere, have demonstrated a seasonal variation in urinary calculi formation 1, 4.

An understanding of factors such as seasonal variation in the formation of urinary calculi has implications for health care planning as well as the management and advice given to patients. Australia is the world's driest inhabited continent5, and Canberra in Australia has a well define four seasons variation; if a seasonal effect is universal and temperature-dependent then we expect an increase in renal colic visits in the warmer months. The purpose of this study was to determine if urolithiasis presentations in an Australian hospital exhibited seasonal patterns.

Method

This is a retrospective review of acute renal colic presentations to the emergency department at The Canberra Hospital. The hospital is a tertiary referral centre which provides specialist and acute care to more than 500,000 people in Australia Capital Territory (ACT) and surrounding South-Eastern New South Wales. Eligibility for the study was defined as those individuals presenting with new acute renal colic with radiologically-confirmed urolithiasis, re-presentations were excluded. Information was collected from hospital records regarding patient demographics, personal past history of renal colic and details of management. Climatic data for the ACT during this period were retrieved from the Australian Bureau of Meteorology and seasonally correlated to renal colic presentations. The data was analysed using goodness of fit tests to assess for statistical significance. A p-value < 0.05 was considered statistically significant. Statistical analysis was performed using the R statistic package (R Development Core Team, Vienna, Austria).

Results

A total of 637 patients presented with radiologically confirmed urolithiasis from 1st January 1998 to 31st December 2007. The ratio of male to females was 2.8:1. Middle aged males and females aged between 40 to 59 years, showed the highest rate of presentation. Overall 37.4% had a previous history (Table 1).

Season, temperature and humidity (Figure1 and Figure 2) We found a significant association between the number of presentations and the season (÷2=31.27, df=3, p < 0.001) with a significantly higher number of presentations in autumn months. Presentation was most common in the Australian autumn months, namely between March and May (32.8%), with the fewest documented cases of primary urolithiasis during the Australian winter months between June to August (18.7%). However, highest temperature or lowest humidity does not appear to have a direct influence on the number of presentations.

Stone size (Table 2)

At presentation the majority of calculi were small (53.8% <5mm) and located within the distal ureters (47.4%). There is no association between stone size and season of presentation (p=0.26). Stone size is significantly related to management approach (÷2=154.06, df=2, p < 0.001). Conservative measures are instituted significantly more often when stone size is ? 5mm. There is a significant association between location of stone and management instituted (÷2= 155.56, df = 3, p < 0.001). Stones in the proximal ureter are managed surgically significantly more often (p<0.001), while stones located in the distal ureter were managed conservatively for a greater majority or the time (p<0.001).

Discussion

Our study has shown a seasonal variation in presentations of urolithiasis. Presentations were highest during the Australian warmer months December to May. During the study period the mean maximum temperatures in the ACT ranged from 28.3°C in summer to 13.1°C in winter, likewise humidity ranged between 36.0% in summer to 56.0% in winter. When humidity is low, moisture on skin can evaporate freely. If the temperature is also high the body's ability to cool through the evaporation of perspiration is diminished. Higher average temperatures during summer could lead to increased water loss through perspiration and lower urine volume. During the warmer months dehydration through perspiration is therefore thought to play an important role in calculus formation7. Bescolo-Berto et al8 recently demonstrated a negative correlation between humidity and renal colic using computer modeling. An association was made between the onset of renal colic and exposure to hot and dry weather. This effect was higher when temperatures rose above 27°C and relative humidity fell below 45%. During the summer months in the ACT region, both the average maximum temperatures and the average relative humidity levels were above this threshold.

Nevertheless, one of the main differences from previous studies is that presentations in our study were not highest during summer, the warmest period; rather a peak was seen during the autumn months. The kinetics of stone formation is poorly understood. The length of time required for calculus formation, and period between exposure and symptomatic urinary stones have not been defined. It is possible that differences in length of exposure to warm and dry periods accounts for the discrepancy. Our findings suggest that a lag period exists between exposure and manifestation as renal colic. We speculate that stones start forming during the hot summer months until they reach a critical size to cause symptoms before presentation, and hence the lag in presentation during autumn.

Our study also showed that patients with stones more than 5mm and proximal ureteric stones are more likely to have surgical interventions rather than conservative management, as the chances of these stones being passed spontaneously are less likely as compare to smaller (< 5mm) and distal ureteric stones respectively9. This is conforming to the American Urological Association (AUA) guideline. Therefore, we expect much higher stone case workload during the summer and autumn months.

The findings from this study suggested that stone cases workload increases by 1.5 times during summer and autumn seasons as compared to winter and spring seasons. We believe these findings may have an impact on planning of the future healthcare provision as well as patient's education strategies. Arguably, timely health campaigns for renal stone prevention such as patients information campaign to encourage increase fluid intake to >2L per day or achieve urine output >2.5L per day11 should be instigated during summer and autumn seasons. In addition, healthcare provision for stone management should be increase during the summer and autumn seasons, such as, a transient increase in operating time slots for stone cases and more effective use of mobile lithotripsy service, in order to reduce the number of ureteric stents in situ and its associated complications10 as well as reduces number of renal tract stones left in situ which can potentially cause infection, hospitalisation associated burden of health care and number of days off work by patients.

Conclusion

This study has demonstrated an association between the presentation of urolithiasis and season. It is suggested that a lag period exists between exposure to warmer and drier periods and manifestation as renal colic. This means an increase in urinary tract stone workload during this period. Therefore, healthcare prevention and dynamic healthcare planning should be instigated to reduce socioeconomic burden secondary to sharply increases of stone case presentations due to a predictable seasonal variation pattern.

References

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2. Holman CD, Wisniewski ZS, Semmens JB, Bass AJ. Changing treatments for primary urolithiasis: impact on services and renal preservation in 16,679 patients in Western Australia. BJU Int. 2002 Jul; 90(1):7-15.

3. Meschi T, Schianchi T, Ridolo E, Adorni G, Allegri F, Guerra A, et al. Body weight, diet and water intake in preventing stone disease. Urol Int, 2004; 72 Suppl 1:29-33

4. Chauhan V, Eskin B, Allegra JR, Cochrane DG. Effect of season, age, and gender on renal colic incidence. AM J Emerg Med, 2004 Nov; 22(7):560-3.

5. Nowak R, The continent that ran dry. The New Scientist, 2007:194(2608):8-11.

6. Australian Bureau of Meteorology: Climate Data Online Climate statistics for Australian locations: Canberra City (Accessed 01 July 2008). Available from: www. abs.gov.au.

7. Basiri A, Moghaddam SM, Khoddam R, Nejad ST, Hakimi A. Monthly Variations of Urinary Stone Colic in Iran and its relationship to the Fasting Month of Ramadan. J Pak Med Assoc 2004; 54(1):6-8.

8. Boscolo-Berto R, Dal MF, Abate A, Arandjelovic G, Tosato F, Bassi P. Do Weather Conditions Influence the Onset of Renal Colic? A Novel Approach to Analysis. Urol Int 2008; 80(1):19-25

9. Segura JW, Preminger GM, Assimos DG, Dretler SP, Kahn RI, Lingeman JE, et al. Ureteral Stones Clinical guidelines panel summary report on the management of ureteral calculi. The American Urological Association. J Urol 1997; 158(5):1915-21

10. Tolley D. Ureteric stents, far from ideal. Lancet 2000; 356(9233):872-3

11. Fink HA, Akornor JW, Garimella PS etal. Diet, fluid, or supplements for secondary prevention of nephrolithiasis: A systematic review and meta-analysis of randomized trials. Eur Urol. 2009 Jul; 56(1): 72-80

PEER REVIEW

Not commissioned. Externally peer reviewed.

CONFLICTS OF INTEREST

Nil.

Author affiliation:

Albert Tiu1, Vincent Tang1, Samuel Gubicak2, Paul Knight1 and Hodo Haxhimolla1

1Department of Urology, The Canberra Hospital, Australian Capital Territory, Australia

2Australian National University, Canberra, Australian Capital Territory, Australia

Corresponding Author:

Vincent Tang

The Canberra Hospital

Yamba Drive

Garran 2605

Australia

Vtang77@gmail.com