The relationship between seasonality, latitude and tuberculosis notifications in Pakistan

Abstract

Background Pakistan ranks amongst the top 20 highest burden tuberculosis (TB) countries in the world. Approximately 369,548 cases of TB (all forms) were notified in 2018, with an estimated incidence of 265 per 100,000 people per year. In other settings, TB has been shown to demonstrate seasonal variation, with higher incidence in the spring/summer months and lower incidence in the autumn/winter; the amplitude of seasonal variation has also been reported to be higher with increasing distance from the equator. Methods Notifications of newly-diagnosed pulmonary and extrapulmonary TB cases were obtained for 139 districts in Pakistan from 2011 to 2017. Data were provided by the Pakistan National TB Control Programme, Islamabad, Pakistan. Statistical analyses were performed to determine whether there was seasonal variation in TB notifications in Pakistan; whether the amplitude of seasonal variation in TB notifications varied according to latitude; whether the amplitude of seasonal variation of TB in Pakistan differed between extrapulmonary TB vs. pulmonary TB. To assess the quarterly seasonality of TB, we used the X-13-ARIMA-SEATS seasonal adjustment programme from the United States Census Bureau. The mean difference and corresponding 95% confidence intervals of seasonal amplitudes between different latitudes and clinical phenotype of TB were estimated using linear regression. Results TB notifications were highest in quarter 2, and lowest in quarter 4. The mean amplitude of seasonal variation was 25.5% (95% CI 25.0 to 25.9%). The mean seasonal amplitude of TB notifications from latitude 24.5°N- < 26.5°N was 29.5% (95% CI 29.3 to 29.7%) whilst the mean seasonal amplitude of TB notifications from latitude 34.5°N - < 36.5°N was 21.7% (95% CI 19.6 to 23.9%). The mean seasonal amplitude of TB notifications across Pakistan between latitudes 24.5°N to 36.5°N reached statistically significant difference (p < 0.001). The amplitude of seasonal variation was greater for extrapulmonary TB (mean seasonal amplitude: 32.6, 95% CI 21.4 to 21.8%) vs. smear positive pulmonary TB mean seasonal amplitude: 21.6, 95% CI 32.1 to 33.1%), p < 0.001. Conclusion TB notifications in Pakistan exhibit seasonal variation with a peak in quarter 2 (April–June) and trough in quarter 4 (October–December). The amplitude of seasonality decreases with increasing latitude, and is more pronounced for extrapulmonary than for pulmonary TB.

Estimating the Effects of the COVID-19 Outbreak on the Reductions in Tuberculosis Cases and the Epidemiological Trends in China: A Causal Impact Analysis

“…36 An earlier systematic review indicating that a seasonal variation of TB was predominantly found during the spring based on 12 studies performed between 1971 and 2006 from 11 countries/regions worldwide also lends support to our current finding. However, our results showed inconsistency with those in Pakistan and Ethiopia (peaking in April-June), 37,38 Japan (which had a semiannual seasonal variation peaking in June-December, apart from November), and Tunisia (peaking in winter and spring). 39 This discrepancy may be attributable to the different geographical distributions, socioeconomic status, healthcare facilities, climatic conditions, and lifestyles of residents.…”

The Impact of the Seasonal and Geographical Distribution of Tuberculosis in Sicily: A 6-Year Retrospective Study (2018–2023)

“…It has been observed that the occurrence of TB varies seasonally in several populations and countries with different incidence levels. This phenomenon has been reported since as early as the 1930s, and has recently been highlighted in European and other countries, showing the seasonal variation of TB disease [ 54 , 55 , 56 , 57 , 58 ].…”

“…Investigating the correlation between the incidence of TB notification cases and the season has yielded insightful results [ 54 , 55 , 56 , 57 , 58 , 60 ]. Our findings indicate a higher prevalence of TB diagnoses during the months of autumn.…”

Tuberculosis epidemiological trend in Sousse, Tunisia during twenty years (2000–2019)

“…Among these comorbidities, diabetes has been linked to increased risks and adverse tuberculosis treatment outcomes [ 18 , 24 , 25 ]. Environmental factors have been also incriminated in the tuberculosis genesis such as air pollution [ 26 ] and seasonality [ 14 , 15 , 27 ]. In Sousse, Tunisia, the tuberculosis incidence increasing trend can also be explained by the above-described factors, as the population is aging [ 28 ], and there is a quite high prevalence of smoking and diabetes [ 17 , 29–31 ].…”