Introduction {#sec1-1}
============

Hepatitis E is an inflammatory liver disease caused by a non-enveloped positive-sense \[[@ref1]\] and single-stranded ribonucleic (RNA) genome called the hepatitis E virus (HEV). The virus is in four different types identified as genotypes 1, 2, 3 and 4. Genotypes 1 and 2 have been isolated in humans while 3 and 4 are found in animals. HEV is transmitted mainly through faecal contamination of drinking water and uncooked foods. Generally, the risk factors of the disease include lack of access to cheap, safe and potable drinking water, unhygienic living conditions and indiscriminate disposal of human wastes, poverty, the insecurity that results to a strain on access to basic life amenities and limited access to quality health services \[[@ref2]\]. Symptoms of the disease include mild fever, anorexia, nausea, jaundice, dark urine, pale stools and slight liver inflammation, although, rare cases have been reported to result to fulminant hepatitis in pregnant women \[[@ref3]\], \[[@ref4]\]. Diagnosis of HEV infection includes detection of the HEV in stool or serum samples and serological tests for identification of anti-HEV Ig G and Ig M \[[@ref1]\]. Measures to be taken to eliminate the risk factors are consistent supply of clean and safe water, improving personal hygiene and ensuring proper disposal of human wastes.

Hepatitis E is one of five known human hepatitis viruses. Others are A \[[@ref5]\], B \[[@ref6]\], \[[@ref7]\], C \[[@ref8]\], \[[@ref9]\], \[[@ref10]\] and D \[[@ref11]\]. The prevalence of HEV is very low compared with the others, especially hepatitis B virus (HBV). Numerous articles that investigated different aspects of HBV infections in Nigeria \[[@ref12]\], \[[@ref13]\], \[[@ref14]\] and few papers are available for HEV infection.

This paper aims to present a statistical analysis of a few articles published on the prevalence of HEV infection in Nigeria. The few papers are traceable to the low prevalence of the disease in the world of which the studied country is a particular case. A similar investigation has been done and can be found in \[[@ref15]\], \[[@ref16]\], \[[@ref17]\], \[[@ref18]\], \[[@ref19]\], \[[@ref20]\], \[[@ref21]\].

Material and Methods {#sec1-2}
====================

Study Design {#sec2-1}
------------

The study design is Web of Science, Scopus and PubMed databases. The keywords "Hepatitis E" OR "HEV" AND "Nigeria" were queried in Scopus, PubMed and Web of Science databases. PubMed, Scopus and Web of Science (WOS) returned 301, 66 and 11 articles respectively. Further evaluation showed that the articles in WOS are also contained in Scopus and are littered with hepatitis B and studies on areas not related to Nigeria. A final seven (7) articles were sieved out after all the unrelated articles were removed.

Eligibility Criteria {#sec2-2}
--------------------

The papers that contained the prevalence of HEV in their abstracts were included. Risk of bias was almost nonexistent since the sample size is small.

Ethics Statement {#sec2-3}
----------------

No ethical rules were violated. All the sources of information were duly acknowledged.

Statistical Analysis {#sec2-4}
--------------------

The absence of numerous studies places undue restrictions on the use of different statistical techniques. The statistical techniques are needed to reveal hidden patterns as long as the sample size is appreciably high \[[@ref22]\], \[[@ref23]\], \[[@ref24]\], \[[@ref25]\], \[[@ref26]\], \[[@ref27]\], \[[@ref28]\]. The 7 articles were analysed using Minitab version 17.0, binary logistic regression was used for the analysis, and this was as a result of splitting of the target groups into two distinct and non-overlapping classes. P-value of 0.05 was considered significant.

Results {#sec1-3}
=======

The summary of the data presentation of the 7 articles \[[@ref29]\], \[[@ref30]\], \[[@ref31]\], \[[@ref32]\], \[[@ref33]\], \[[@ref34]\], \[[@ref35]\] are presented in [Table 1](#T1){ref-type="table"}. The publication span 10 years. It can be seen that (6/7) of both the methodology and diagnostics (tool for analysing serum and faecal samples) used in the articles are cross-sectional studies and enzyme-linked immunosorbent assay (ELISA) technique respectively.

###### 

Studies on hepatitis E virus infection in Nigeria

  Author         Publication Year   Methodology       Target Group       Diagnostics   Sample size   HEV positive
  -------------- ------------------ ----------------- ------------------ ------------- ------------- --------------
  \[[@ref29]\]   2008               Observation       Hospitalized       Therapy       1             1
  \[[@ref30]\]   2013               Cross sectional   Non-hospitalized   ELISA         132           36
  \[[@ref31]\]   2014               Cross sectional   Pigs               ELISA         90            69
  \[[@ref32]\]   2014               Cross sectional   Non-hospitalized   ELISA         462           43
  \[[@ref33]\]   2015               Cross sectional   Non-hospitalized   ELISA         406           31
  \[[@ref34]\]   2018               Cross sectional   Pigs               ELISA         120           69
  \[[@ref35]\]   2018               Cross sectional   Non-hospitalized   ELISA         177           16

Prevalence of HEV in the samples {#sec2-5}
--------------------------------

HEV positive means the presence of anti-HEV IgG or HEV RNA in the study samples. The prevalence for each case is obtained using the dataset of [Table 1](#T1){ref-type="table"}, by dividing the total number of HEV positive and the total number investigated and multiplying by 100. This is presented in [Table 2](#T2){ref-type="table"}.

###### 

Prevalence of the two types of HEV infection in Nigeria

                       Humans   Animals
  -------------------- -------- ---------
  Total investigated   1178     210
  HEV positive         127      138
  Prevalence           10.8%    65.7%

Correlation Analysis {#sec2-6}
--------------------

Correlation coefficient was obtained between the target group (humans = 0, animal = 1) and the HEV positive and it was computed to be (r = 0.327, p = 0.474).

Binary Logistic Regression {#sec2-7}
--------------------------

Binary logistic regression was performed to determine the association between the target group y (humans = 0, animal = 1) and the HEV positive (x).

This is to determine if the prevalence of HEV can predict whether the target group is animal or human.

The details are presented in Tables [3](#T3){ref-type="table"} to [7](#T4 T5 T6 T7){ref-type="table"}, and the logistic regression equation is Exp(y) = -2.33+0.338x.

###### 

Deviance table

  Source DF Adj Dev Adj Mean Chi-Square P-Value
  -----------------------------------------------
  Regression 1 0.7842 0.7842 0.78 0.376
  Error 5 7.5915 1.5183
  Total 6 8.3758

###### 

Model Summary

  --------------------
  Deviance Deviance\
  R-Sq R-Sq(adj) AIC
  --------------------
  9.36% 0.00% 11.59

  --------------------

###### 

Coefficient of the model

  Term Coef SE Coef VIF
  -----------------------
  Constant -2.33 2.04
  x 0.0338 0.0407 1.00

###### 

Odds Ratios for Continuous Predictors

  Odds Ratio 95% CI
  ---------------------------
  x 1.0344 (0.9550, 1.1204)

###### 

Goodness-of-Fit Tests

  Test DF Chi-Square P-Value
  ------------------------------
  Deviance 5 7.59 0.180
  Pearson 5 6.61 0.252
  Hosmer-Lemeshow 4 4.60 0.330

Discussion {#sec1-4}
==========

The few available studies on HEV infection in Nigeria is due to the less severe nature of the disease when compared with Hepatitis B infection. The low research activities on HEV can also be as a result of the low incidence of the disease, self-medication, the use of traditional or alternative medicine and non-hospitalization. Hospital records about the HEV infection will encourage cross-sectional and retrospective studies.

The risk factors available from the few articles are consistent with the global epidemiology of HEV infection. The risk factors are faecal contamination of water and food, improper disposal of human and animal wastes, poverty, unhygienic environment and inadequate access to quality healthcare services.

Serum and faecal analysis of blood and stool samples of 1178 humans and 210 pigs (animals) were done, and the presence of anti-HEV IgG or HEV RNA in the study samples were 127 and 138 respectively. Further analysis showed the prevalence of HEV are 10.8% and 65.7% in human and animals, respectively. The high level of the prevalence in animals calls for urgent action to avoid infections to human via faecal oral transmission.

There is a weak positive non-significant association between the target groups (humans and animals) and the HEV infection (positive). This is the outcome of the prevalence that showed that the prevalence of both groups is different; that is, high for animals and low for humans.

The application of binary logistic regression yielded an equation that can be used to predict the target group from the HEV positive humans or animals. Generally, the logistic model was not statistically significant (p-value = 0.376), and the model was able to explain only 9.3% of the deviation or variability of the dependent variable. The odds ratio was gotten to be; OR = 1.0344 (0.9550, 1.204) 95% CI. Thus, in Nigeria, the odds of prevalence of HEV in animals are 1.0344 higher than humans.

The authors appreciate the efforts of the anonymous reviewers toward this publication. The support from Covenant University, Nigeria, is also deeply appreciated.

**Funding:** This research was financially supported by Covenant University, Nigeria

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