Seroprevalence of Salmonella Typhi among School Children

Original Article

Seroprevalence of Salmonella Typhi among School Children in Marawe Area in Northern Sudan

Ahmed M. Z. Abdalwahid^1*, Arwa M. O. Ahmed¹, Nadia I. M. Salih¹

Abstract

Background: Salmonellosis is a major global health problem, especially in developing countries. It is a food/water-borne disease in humans. The study was conducted to determine the prevalence of Salmonella seropositivity and risk factors for transmission among school children in Marawe area in northern Sudan.

Materials and Methods: This cross-sectional study was conducted between March and July 2021. The study targeted 310 healthy school children, who were recruited using a convenience sampling technique. Five ml of venous blood samples were collected from each child and were examined for Salmonella Typhi (S. typhi) seropositivity using the Widal test.

Results: A 100% response rate was obtained; of them, 119 (68%) were females. The results showed that 134 (43%) participants tested positive for S. typhi, with higher seropositive cases among children from rural areas (64%), and the age 6-10 years was the most affected age group (61%). Also, the study revealed that living conditions such as the type of toilet, as well as children eating vegetables and fruits without washing, eating street food, and not practicing regular hand hygiene tended to have higher seropositivity rates and reached statistical significance as risk factors for Salmonella seropositivity.

Conclusion: Considering the relatively high Salmonella seropositivity rate in the study area compared to regional data, the state authorities should provide a safe water supply and improve health education for society on prevention and control of acquiring S. typhi seropositivity.

Keywords: Seroprevalence, Salmonella seropositivity, Typhoid fever, School children, Risk factors, Sudan.

________________________________________________________________________

1Deptartment of Microbiology, Faculty of Medicine, Dongola University, Dongola City, Northen State, Sudan
*Corresponding Author: Ahmed Mohamed Zein Abdalwahid. Deptartment of Microbiology, Faculty of Medicine, Donogla University, Dongola City, Northen State, Sudan Email: ahmedziin@yahoo.com

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:Introduction

Salmonellosis is a common form of food/water borne disease in humans. Salmonella species are Gram-negative, non-spore forming rod-shaped bacteria and are a member of Enterobaceriaceae.(1) The disease continues to be a major health problem in developing countries. In recent years there has been a global increase in Salmonella enteritis seropositivity.(2) The World Health Organization (WHO), in 2019 estimated that more than nine million people get sick from typhoid, resulting in about 110 000 deaths per year occur globally.(3)

Studies have suggested that, consumption of contaminated eggs and/or poultry meat was the reason for this global increase.(4) The bacterium can be transmitted through fecal oral route, where humans may acquire the disease through contaminated food and water.(5)

Salmonella colonize the distal ileum and proximal colon. The infective dose for salmonellosis that is capable of establishing Salmonella seropositivity in the mucosa of the small intestine ranges from 10 to 10⁵ cells.(6) Salmonella serovars causing illness in humans are grouped into two, Salmonella enterica-serovars referred to as typhoid salmonella (S. typhi and S. paratyphi) and other grouped as

. non-typhoid salmonella (NTS)

The typhoid salmonella characterized by fever, gastroenteritis and complications such as septicemia, leucopenia, immunological and neurological symptoms, that may lead to death.(7) On the other hand, the NTS usually cause non-fatal illnesses

. often restricted to gastroenteritis, nausea, vomiting and diarrhea

The risk for Salmonella seropositivity is very high in low-income countries due to poor-hygiene and lack of access to safe foods and water supply.(8) People of all ages are susceptible to Salmonella seropositivity, however, the elderly, infants and immunocompromized patients are at great risk of Salmonella seropositivity and generally have more severe symptoms.(1)

Blood culture is the gold standard method for diagnosis S. typhi and S. paratyphi seropositivity. Serologically, salmonella is classified into six serotypes which are detected on the basis of their antigenicity. Usually, NTS seropositivity does not require treatment with antibiotic drugs, however, seropositivity caused by S. typhi and S. paratyphi require treatment with antibiotics such as Cefixime, Chloroamphenicol, Amoxicillin and Azithromycin.(9)

In Sudan, isolation of salmonella was documented by different investigators.(10,11,12,13) The Global Burden of Disease study estimates that, in 2019, Sudan had 16,326 typhoid cases or 40 cases per 100,000 population, 50% of which were among children under 15 years of age; and 224 typhoid deaths, 60% of which were among children under 15 years of age.(14)

The distribution of salmonella serovars in Sudan varies geographically. However, S. typhi was the most commonly reported. The bacterium was recovered from humans, cattle, camel and poultry.(15) The disease is prevalent in several States in Sudan and antibiotic resistance has been reported in different patterns.(16) The study aimed to determine the Seroprevalence of Salmonella seropositivity (enteric fever) among healthy school children in Marawe area and identify the risk factors

. for transmission

Material and Methods

Study design and area

This was a cross-sectional study conducted from March to July 2021, in Marawe area, Northern Sudan. Farming and crop production are the major occupations of people in the study area. Livestock reared include sheep, goats, cattle, camels, and

. poultry

Study Population and Sample Size

The study was limited to healthy children attending Marawe primary school aged between six to 15 years. The sample size was calculated as 310 using a sample size calculator with a 95% confidence level and 5% margin of error.(17)

Sample Collection and Laboratory Procedure

Five mls venous blood were collected from participants into vacutainer tubes containing no preservative/additive and test performed using the Widal slide agglutination method. Collected blood samples were centrifuged and only 50 uL of serum were transferred using calibrated pipette on each circle of Widal plate, which consisted of 8 rows of circles. A drop of the reagent (TO, AO, CO, TH, BH and CH) respectively was added beside each drop of serum. Each drop of reagent was mixed with a drop of serum in a circular manner, using a separate mixing stick for each. The Widal plate was gently swirled in a circular manner and macroscopically visualized for agglutination within 2 minutes. Positive results were indicated by the appearance of a visible agglutination within a minute formed due to a reaction occurring between antibodies present in the serum samples and antigen- specific for S. typhi and S. paratyphi. Results were recorded as 1/40, 1/60, 1/80, 1/160, depending on the concentration of the agglutination observed. A titer of O and H antigens greater than 1:60 to 1:130 was considered positive. Negative results were

. indicated by the absence of the agglutination (Non-reactive)

Questionnaire Survey

The participants were interviewed by the researchers. A structured questionnaire was administered to the participants to collect socio-demographic data (gender, age, education level, residence, and occupation), living conditions (types of toilets and water supply) and risks behaviors (personal hygiene, eating habits). Data were entered into Statistical Software Package (SSPS version 22) for statistical analysis

. using Chi Square Test

Ethical Consideration

Ethical clearance was obtained from the State Ministry of Health and Education. Written consent was obtained from school headmasters and parents or guardians

. of the children. Confidentiality of the study participants was maintained

Results

Socio-demographic Characteristics of Participants

Table 1 shows details of the Socio-demographic characteristics of the study sample. Most of the participants (56%) were females, and 56.5% were 6-10 years old. Eighty percent of the participants’ fathers/guardians had more than a primary school

. education and were mostly employed. (Table 1)

Table (1): Socio-demographic characteristics of the Participants (n=310)

Living Conditions and Risks Behaviors among Participants 

Table 2 shows details of the living conditions of the participants and risks factors for salmonella contamination. The sources of drinking water identified by participants included pipe-borne (78%) and directly from the river (22%).Pit latrines were used by 54% of households. Moreover, 83% of the participants admitted of not regularly washing their hands with soap after defecation

 Only 43% wash vegetables and fruits before eating

Table (2): Living Conditions and Risk Behaviors among the Study Participants (n=310)

Prevalence of Salmonella Seropositivity

A titer of O and H antigens of 1:60 to 1:130 or greater was considered positive for S. typhi. Of the sample study, 134 out of 310 (43%) tested positive for S. typhi. Table 3 shows the sociodemographic characteristics of the affected participants. All variables were significant risk factors for seropositivity (P-value range between .0000 and .002) except for the Occupation of the father/guardian, where the P-value was .34. (Table 3)

Table (3): Participants' Sociodemographic characteristics and seroprevalence

. of Salmonella typhi (n=310)

Table 4 depicts the prevalence of S. typhi seropositivity according to the living conditions and the participants’ hygiene. The presence of pit latrines in the households of affected participants, not washing hands with soap after defecation, not washing vegetables and fruits before eating, and not trimming fingernails all stood out as clear positive risk factors for Salmonellosis (P value < 0.05). The source of water supply had no correlation with the prevalence of Salmonella

. seropositivity

Table (4): Participants Living Conditions, Hygiene, and Seroprevalence of S. typhi (n=310)

Discussion

S. typhi and S. paratyphi specifically affect humans, leading to a severe disease called enteric fever, producing clinical syndromes referred to as typhoid and paratyphoid fever. The present study demonstrated a high percentage of S. typhi among school-aged children in Marawe area, Northen Sudan (43%). This result was higher when compared with studies reported from Kenya (20.3%), Ethiopia (21.7%) and Tanzania (10.3%).(18,19,20)

The study revealed that Salmonella seropositivity was more prevalent among females than males. Similar findings were found by Crump and Mintz.(21) However, this result contrasts with several other studies that reported that males and females were at risk with a relatively equal chance of being affected by the disease.(19,22,23) When considering age groups of affected children with salmonella seropositivity, our study showed an observed difference between the age groups, where (61%) of children aged 6-10 years had a seropositivity compared to (31%) of children aged 11-15 years. However, the statistical analysis for this variable was not done due to missing data (18% of the seropositive children didn’t mention their age). However, this observed difference agreed with the findings reported by Ghosh, Rahman, and Damtew.(24,25,26) Children have been identified as a population at risk for salmonella seropositivity because of their immature immune systems and lack of good hygiene habits.(27) Considering residence, our study showed that participants from rural areas had a higher observed probability of salmonella seropositivity than urban (62% versus 38%), which has been confirmed by the statistical significance. The claim that rural communities have a higher rate of salmonella seropositivity was also reported by other researchers such as Eba and Breiman.(19,28) This might be related to inadequate safe water supply, poor sanitation, and poor quality of life in rural areas.(25,29) Education of parents/guardians plays a key role in preventing and controlling Salmonella seropositivity.(30,31) Eighty percent of parents/guardians in our study group were reasonably educated, which will help with health education in preventing

. infectious diseases

Regarding the water source, the present study revealed that the majority of the affected participants (73%) used pipe water, which may indicate that water got polluted thereafter, a situation that further analysis of the pipe water in the area. However, globally, it is well known that polluted water plays an important role in outbreaks of typhoid fever because fecal matter may gain access to rivers and wells.(23,30,32,33) The present study observed a high prevalence of Salmonella seropositivity among participants using pit latrines (71%) compared to those using flush toilets (29%). This agrees with studies conducted by Charles, Breiman, Ashebir, Cecilia, and Damtew.(34,28,35,36,26) Using proper flush toilets instead of pit lanterns will create less contamination. Also, the study revealed that participants who did not regularly wash their hands before eating vegetables and fruits and regularly eating street food were at risk for Salmonella seropositivity. Similar findings were reported by Medina and Mujca.(37,38) This might be due to surface contamination of vegetables and fruits, that may occur during harvest, market place or street where vendors have limited facilities for storing food and cleaning dishes. This poor hygiene is a vehicle for disease contamination. The proportion of participants seropositive for typhoid was higher among those who did not regularly wash their hands with soap after defecation and had untrimmed fingernails. Similar findings were reported by Cecilia and Jensen.(36,39) Targeting to improve sanitation and access to clean water at schools and for any defined

. population may considerably reduce S. typhi transmission to this area

Conclusion

In conclusion, results showed a high prevalence of Salmonella seropositivity among school children in the study area. It also revealed that females were significantly affected more than males, and using pit latrines in the household and not practicing hand hygiene were significantly associated with acquiring Salmonella seropositivity. Providing a safe water supply and school- and community-based health education regarding good personal hygiene and sanitary practices are imperative in those communities to reduce the transmission and

. morbidity of Salmonella seropositivity

Acknowledgment 

 We gratefully acknowledge the contributions made by the Marawe community, the Headmasters, parents/guardians as well as the district head of Marawe locality for their cooperation during the study period. We would like also to thank the Ministry of Health and Education, Northern State, Sudan, for their generous collaboration

. We also thank the participants for their voluntary participation

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