Study investigating the clinical manifestations of Rift Valley fever in humans: Systematic review and meta-analysis

Permanent identifier


Data extraction in this study was aimed at achieving three main purposes:

  1. Obtain data that describe the characteristics of the included studies
  2. Obtain data for assessing the quality of included studies
  3. Obtain data for synthesizing the frequency and duration of clinical manifestations and duration of illness since onset to diagnosis.

Information was abstracted on the characteristics of eligible studies including first author’s surname, year of publication, type of article (abstract or full text), list of countries where the study was conducted, information on the study design (cohort, cross sectional/outbreak investigation, intervention studies, case series, reviews); demographics (number of participants that were enrolled, age, sex and nationality); laboratory tests used to confirm diagnosis of RVF (enzyme linked immunosorbent assay or ELISA (IgM & IgG), real-time polymerase chain reaction (rtPCR) or quantitative polymerase chain reaction (qPCR), plaque reduction neutralisation test (PRNT) and focus reduction neutralisation test (FRNT) or other serological and viral antigen tests etc). Data on the number or proportion that had co-infections and type of co-infection such as hepatitis B, malaria, schistosomiasis etcetera were also captured. Rift Valley fever presents among humans in form of clinical syndromes including the general febrile syndrome, hepatic or abdominal syndrome, encephalitis syndrome, visual syndrome and haemorrhagic syndrome. Data was collected on several RVF clinical manifestations in humans for which proportion or description of symptoms was recorded. Data was also extracted on the frequency and levels of each laboratory parameter reported.

Data collection methods

Electronic bibliographic databases including Medline/PubMed, Embase, Global Health and Web of Science were searched to identify relevant studies. Two people independently reviewed the abstracts of relevant papers to determine study eligibility and selected the articles for full text review and data extraction. All records from the search and selection process were captured directly into a systematic review flow schema. Data from eligible studies was extracted into two excel sheets. The two reviewers that assessed eligibility were the same persons that extracted the records from the papers. Discrepant entries between the two reviewers were resolved through discussions which were held face to face, by telephone, skype or email and the final agreed records were summarised on the excel sheets. Where two or more manuscripts report data from the same study, these were considered as one study and data was extracted on clinical manifestations that do not duplicate.

Data analysis and preparation

The number of articles obtained through searching, number selected and number from which data was extracted was recorded and presented in a flow diagram. The studies from which data was extracted were identified by the first author’s surname. Data from the excel sheets was imported into stata analysis software. Where two or more studies were available for a particular clinical manifestation, pooled proportions of patients were presented with the parameter and their 95% confidence intervals estimated using random effects models. Sensitivity analysis was done to check the effect of study quality and study design on the pooled proportion. Forest plots were drawn where two or more studies reported a particular clinical manifestation and these were summarised by patient source.

Geographic regions

Studies included in this review came from Africa, the Arabian Peninsula, and the United States of America.

Key dates

13th October 2019 to 31st June 2020

Quality controls

A quality assessment tool by Hoy and Brooks et al was adapted and modified for this study.

The tool evaluated both the internal validity (six parameters) and external validity (two parameters) of the studies. The criteria for assigning low or high risk of bias for each parameter within the tool was modified from the original table by Hoy and Brooks et al to suit the clinical presentation of Rift Valley fever disease.

The assessment of external validity essentially focused on investigating whether there was selection bias and non-response bias in the article. This was achieved by assessing whether the study’s population included all ages and sexes, and non-response bias was minimal.

Internal validity was assessed by ascertainment of whether there was measurement bias and bias in relation with the analysis. This included evaluation of whether the data was collected from the patients themselves or from the proxy, use of case definition, pre-testing or validity and reliability assessment of the data collection instrument, uniformity in data collection, time lapse between the occurrence of clinical symptoms and interview and whether the analysis used appropriate numerators and denominators.

An overall assessment of risk of bias of the article was made basing on the reviewer’s individual judgement, which is in line with the Cochrane and the Grades of Recommendation, Assessment, Development and Evaluation (GRADE) processes. The reviewers agreed upon a summary judgement by discussing discrepant risk of bias allocations for the items on the tool for each article.


Human population


Most study data was in summary form without patient identifiers. Data from case series was summarised without capturing independent patient identifiers.


Not applicable.


Rift Valley fever, RVF, clinical manifestations, syndromes, humans, Africa, Arabian Peninsula

Language of written material


Project title

Systematic review study protocol investigating the clinical manifestations and long-term complications of Rift Valley fever in humans


The work was conducted at the MRC/UVRI and LSHTM Uganda Research Unit which is jointly funded by the UK Medical Research Council (MRC) and the UK Department for International Development (DFID) under the MRC/DFID Concordant agreement and is also part of the EDCTP2 programme supported by the European Union.

This project was funded by the UK Biotechnology and Biological Sciences Research Council (BBSRC) and the Medical Research Council (MRC)/Department of Health, through the UK Vaccines Network which is a Government Funding Stream (Grant no: 16/107/02).

SL was supported by the PANDORA-ID-NET Consortium (EDCTP Reg/Grant RIA2016E-1609) funded by the European and Developing Countries Clinical Trials Partnership (EDCTP2) programme under the Horizon 2020, the European Union’s Framework Programme for Research and Innovation.

GMW is supported by an Oak foundation fellowship and a Wellcome Trust grant (grant number 203077_Z_16_Z).

Grant number

Grant no: 16/107/02.

Data creators

Forename Surname Faculty / Dept Institution Role
Zacchaeus Anywaine Faculty of Infectious and Tropical Diseases / Department of Clinical Research London School of Hygiene and Tropical Medicine, London, United Kingdom
  • Contact Person
  • Data Collector
  • Data Manager
  • Project Leader
  • Researcher
  • Rights Holder
  • Data Creator
Swaib Abubaker Lule Institute for Global Health University College London, London, United Kingdom
  • Data Collector
  • Project Member
  • Researcher
  • Data Creator
Christian Hansen MRC International Statistics & Epidemiology Group, London School of Hygiene and Tropical Medicine, London, United Kingdom
  • Project Member
  • Researcher
  • Supervisor
George Warimwe Centre for Tropical Medicine and Global Health University of Oxford, Oxford, United Kingdom
  • Project Member
  • Researcher
  • Supervisor
Alison Elliott Faculty of Infectious and Tropical Diseases / Department of Clinical Research London School of Hygiene and Tropical Medicine, London, United Kingdom
  • Project Member
  • Researcher
  • Supervisor

Associated roles

Forename Surname Faculty / Dept Institution Role
Ayoub Kakande Medical Research Council/Uganda Virus Research Institute and London School of Hygiene and Tropical Medicine Uganda Research Unit, Entebbe, Uganda London School of Hygiene and Tropical Medicine, London, United Kingdom
  • Data Creator
  • File Description

    Filename Description Access status Licence Embargo period
    DataExtractionSheet-Proportion_of_RVF_symptoms Data extraction sheet containing proportion of RVF symptoms Open to all Creative Commons Attribution (CC-BY) -
    DataExtractionSheet-Symptoms_clinical_syndromes File contains a description of the clinical presentation (Signs or Symptom) and Laboratory (Blood and CSF) parameters. Also contains information on the duration of symptoms before diagnosis and/or treatment, duration of symptoms from onset of symptoms till resolution, incubation period, patient source and average number of days patients were hospitalised. Open to all Creative Commons Attribution (CC-BY) -