Of the 703 included episodes of acute appendicitis, 366 (52.1%) were associated with male patients and the remaining 337 (47.9%) with female patients. The average admission duration across the study was 3.4 days with an average patient age of 38.
In accordance with National Institute for Health and Care Excellence (NICE) guidelines, all 703 patients underwent either a laparoscopic or open appendicectomy.
January was found to have the lowest observed incident cases of acute appendicitis with only 38 (5.4%) of the episodes occurring in that month, this was a 35.1% reduction on the average. Biostatistical analysis suggested it to be a significantly reduced proportion (p = 0.005).
The month with the highest observed incidence of acute appendicitis was July, recording 73 episodes (10.4%) over the study period. When compared to the expected value this represented a significant increase of 24.6% (p = 0.049).
An annual trend was observed with a lower than expected incidence of acute appendicitis during the winter months (Dec, Jan, Feb), compared to an increased incidence in the late spring and summer (May, Jun, Jul) see Fig. 1.
As could be expected, the average sunlight hours were found to be highest during the summer months and lowest during the winter months see Fig. 2. This climatic indicator displayed high annual variation, the maxima (62.5 hours) representing 360.1% of the minima (225.4 hours).
In January and December there were an average of 62.5 hours and 62.2 hours of sunlight respectively, the lowest two values. This was found to correlate with reduced rates of acute appendicitis compared to the expected value, 48 in December and 38 in January.
The highest number of incident cases, 73 episodes (10.4%) in July, was found to coincide with the greatest average monthly sunlight hours (225.4 hours).
When Pearson correlation coefficient testing was performed, average sunlight hours and incidence of acute appendicitis were found to be weakly positively correlated (r = 0.37, p = 0.24).
The maxima of average rainfall, 73.0mm in January, was found to coincide with the lowest incidence of acute appendicitis.
However, the lowest average rainfall was seen in April (34.6mm) which was associated with 55 episodes. This fell within statistically insignificant deviation from expected values (p = 0.62).. The second lowest average rainfall was seen in July (41.0mm), the month with the highest incidence of acute appendicitis see Fig. 3.
Annual variation in this climatic indicator was lower than sunlight hours, with the maxima 210.9% of the minima.
Statistical testing revealed a weakly negative correlation between average rainfall and incidence of appendicitis (r = –0.15, p = 0.64)..
Average monthly temperature was calculated as the mean of the average maximum and minimum temperatures, in accordance with Met Office guidance9.
The lowest average temperature was noted in January (4.6 Celsius), coinciding with the lowest incidence of acute appendicitis (38). Likewise, the highest average temperate was seen in July (16.8 Celsius), the month with the highest observed incidence see Fig. 4.
Temperature showed very similar annual variation to sunlight hours, with the maxima 365.2% of the minima.
Of the studied climatic indicators, average temperature showed the greatest association with the incidence of acute appendicitis. A moderately positive correlation was found between the two, meeting the threshold for statistical significance (r = 0.58, p = 0.048).. An increase in temperature of 12.2 degrees (from lowest to highest) was associated with a 92.1% increase in the monthly incidence.