Seasonal patterns of tuberculosis case notification in the tropics of Africa: A six-year trend analysis in Ethiopia

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Abstract

Objective

Seasonal variations affect the health system’s functioning, including tuberculosis (TB) services, but there is little evidence about seasonal variations in TB case notification in tropical countries, including Ethiopia. This study sought to fill this gap in knowledge using TB data reported from 10 zones, 5 each from Amhara and Oromia regions.

Methods

Notified TB cases for 2010–2016 were analyzed using SPSS version 20. We calculated the quarterly and annual average TB case notification rates and the proportion of seasonal amplitudes. We applied Winters’ multiplicative method of exponential smoothing to break down the original time series into seasonal, trend, and irregular components and to build a suitable model for forecasting.

Results

A total of 205,575 TB cases were identified (47.8% from Amhara, 52.2% from Oromia), with a male-to-female ratio of 1.2:1. The means of 8,200 (24%), 7,992 (23%), 8,849 (26%), and 9,222 (27%) TB cases were reported during July-September, October-December, January-March, and April-June, respectively. The seasonal component of our model indicated a peak in April-June and a trough in October-December. The seasonal amplitude in Amhara region is 10% greater than that of Oromia (p < 0.05).

Conclusions

TB is shown to be a seasonal disease in Ethiopia, with a peak in quarter four and a low in quarter two of the fiscal year. The peak TB case notification rate corresponds with the end of the dry season in the two agrarian regions of Ethiopia. TB prevention and control interventions, such as efforts to increase community TB awareness about TB transmission and contact tracing, should consider seasonal variation. Regional variations in TB seasonality may require consideration of geographic-specific TB case-finding strategies. The mechanisms underlying the seasonal variation of TB are complex, and further study is needed.

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Most cited references 25

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Health Extension Workers Improve Tuberculosis Case Detection and Treatment Success in Southern Ethiopia: A Community Randomized Trial

Daniel G. Datiko, Bernt Lindtjørn (2009)

Background One of the main strategies to control tuberculosis (TB) is to find and treat people with active disease. Unfortunately, the case detection rates remain low in many countries. Thus, we need interventions to find and treat sufficient number of patients to control TB. We investigated whether involving health extension workers (HEWs: trained community health workers) in TB control improved smear-positive case detection and treatment success rates in southern Ethiopia. Methodology/Principal Finding We carried out a community-randomized trial in southern Ethiopia from September 2006 to April 2008. Fifty-one kebeles (with a total population of 296, 811) were randomly allocated to intervention and control groups. We trained HEWs in the intervention kebeles on how to identify suspects, collect sputum, and provide directly observed treatment. The HEWs in the intervention kebeles advised people with productive cough of 2 weeks or more duration to attend the health posts. Two hundred and thirty smear-positive patients were identified from the intervention and 88 patients from the control kebeles. The mean case detection rate was higher in the intervention than in the control kebeles (122.2% vs 69.4%, p<0.001). In addition, more females patients were identified in the intervention kebeles (149.0 vs 91.6, p<0.001). The mean treatment success rate was higher in the intervention than in the control kebeles (89.3% vs 83.1%, p = 0.012) and more for females patients (89.8% vs 81.3%, p = 0.05). Conclusions/Significance The involvement of HEWs in sputum collection and treatment improved smear-positive case detection and treatment success rate, possibly because of an improved service access. This could be applied in settings with low health service coverage and a shortage of health workers. Trial Registration ClinicalTrials.gov NCT00803322

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Seasonality of tuberculosis in the United States, 1993-2008.

Matthew Willis, Carla Winston, Charles M. Heilig … (2012)

Although seasonal variation in tuberculosis incidence has been described in several recent studies, the mechanism underlying this seasonality remains unknown. Seasonality of tuberculosis disease may indicate the presence of season-specific risk factors that could potentially be controlled if they were better understood. We conducted this study to determine whether tuberculosis is seasonal in the United States and to describe patterns of seasonality in specific populations. We performed a time series decomposition analysis of tuberculosis cases reported to the Centers for Disease Control and Prevention from 1993 through 2008. Seasonal amplitude of tuberculosis disease (the difference between the months with the highest and lowest mean case counts), was calculated for the population as a whole and for populations with select demographic, clinical, and epidemiologic characteristics. A total of 243 432 laboratory-confirmed tuberculosis cases were reported over a period of 16 years. A mean of 21.4% more cases were diagnosed in March, the peak month, compared with November, the trough month. The magnitude of seasonality did not vary with latitude. The greatest seasonal amplitude was found among children aged <5 years and in cases associated with disease clusters. Tuberculosis is a seasonal disease in the United States, with a peak in spring and trough in late fall. The latitude independence of seasonality suggests that reduced winter sunlight exposure may not be a strong contributor to tuberculosis risk. Increased seasonality among young children and clustered cases suggests that disease that is the result of recent transmission is more influenced by season than disease resulting from activation of latent infection.

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Seasonality of tuberculosis: the reverse of other respiratory diseases in the UK.

Kirsty A Douglas, D. W. Strachan, Lara J Maxwell (1996)

In Western societies there is a winter peak in mortality, largely accounted for by respiratory and cardiovascular deaths. In view of the known seasonal variation in vitamin D, and of the postulated link between tuberculosis and vitamin D deficiency, a study was undertaken to examine whether the presentation of tuberculosis had the same seasonal rhythm as other pulmonary infections. Using cosinor analysis the presence or absence of seasonality was determined for 57,313 tuberculosis notifications for England and Wales. OPCS data in four weekly notifications over a 10 year period (1983-92) were examined as two quinquential sets (1983-7 and 1988-92). These were compared with two groups of acute respiratory illness: 138,992 notifications to OPCS of pneumonia deaths for 1988-92 and all admissions to Scottish hospitals with respiratory disease (252,163 cases) during 1980-4. Analysis of notifications of tuberculosis revealed a summer peak with an amplitude of 10%. This pattern differs markedly from other respiratory disorders in which a winter peak and summer trough is observed. The unusual seasonality of tuberculosis is currently unexplained. One possibility is that low post-winter trough levels of vitamin D (which are known to affect macrophage function and cell mediated immunity) might result in impaired cellular immunity leading, after a latent period, to reactivation of dormant mycobacterial infection.

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Author and article information

Contributors

Z. Gashu:

ORCID: http://orcid.org/0000-0002-2774-7628

Role: Formal analysisRole: InvestigationRole: MethodologyRole: SoftwareRole: Writing – original draftRole: Writing – review & editing

D. Jerene: Role: ConceptualizationRole: Funding acquisitionRole: InvestigationRole: Project administrationRole: ResourcesRole: SupervisionRole: Visualization

D. G. Datiko: Role: Data curationRole: MethodologyRole: SupervisionRole: ValidationRole: Writing – review & editing

N. Hiruy: Role: Data curationRole: Investigation

S. Negash: Role: Project administrationRole: Supervision

K. Melkieneh: Role: InvestigationRole: Project administration

D. Bekele: Role: Project administrationRole: Supervision

G. Nigussie: Role: Project administrationRole: Supervision

P. G. Suarez: Role: Project administrationRole: SupervisionRole: VisualizationRole: Writing – review & editing

A. Hadgu: Role: Data curationRole: Software

Thomas Wingfield: Role: Editor

Journal

Journal ID (nlm-ta): PLoS One

Journal ID (iso-abbrev): PLoS ONE

Journal ID (publisher-id): plos

Journal ID (pmc): plosone

Title: PLoS ONE

Publisher: Public Library of Science (San Francisco, CA USA )

ISSN (Electronic): 1932-6203

Publication date (Electronic): 26 November 2018

Publication date Collection: 2018

Volume: 13

Issue: 11

Electronic Location Identifier: e0207552

Affiliations

[1 ] Management Sciences for Health, USAID Challenge TB Project, Addis Ababa, Ethiopia

[2 ] Oromia Regional Health Bureau, Addis Ababa, Ethiopia

[3 ] Amhara Regional Health Bureau, Addis Ababa, Ethiopia

[4 ] Management Sciences for Health, Arlington, Virginia, United States of America

University of Liverpool, UNITED KINGDOM

Author notes

Competing Interests: The authors have declared that no competing interests exist.

‡ ZG and DJ are joint senior authors on this work.

* E-mail: zgashu@ 123456msh.org

Author information

Z. Gashu http://orcid.org/0000-0002-2774-7628

Article

Publisher ID: PONE-D-18-23625

DOI: 10.1371/journal.pone.0207552

PMC ID: 6261032

PubMed ID: 30475836

SO-VID: cf03735b-44f5-4972-afc1-feaf14b1d37c

License:

This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

History

Date received : 10 August 2018

Date accepted : 1 November 2018

Page count

Figures: 4, Tables: 2, Pages: 12

Funding

The United State Agency for International Development (USAID) supported this work through the Help Ethiopia Address the Low TB Performance (HEAL TB) Project, under cooperative agreement number AID-663-A-11-00011. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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Data Availability All relevant data are within the manuscript and its Supporting Information files.

Seasonal patterns of tuberculosis case notification in the tropics of Africa: A six-year trend analysis in Ethiopia

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Most cited references 25

Health Extension Workers Improve Tuberculosis Case Detection and Treatment Success in Southern Ethiopia: A Community Randomized Trial

Seasonality of tuberculosis in the United States, 1993-2008.

Seasonality of tuberculosis: the reverse of other respiratory diseases in the UK.

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