Seroepidemiology of Helicobacter pylori infection in a population of Egyptian children

Abdollah B Naficya, Robert W Frenckb, Remon Abu-Elyazeedb, Yongdai Kimc, Malla R Raoa, Stephen J Savarinob, Thomas F Wierzbab, Eric Hallb and John D Clemensa

a Epidemiology Branch, National Institute of Child Health and Human Development, Bethesda, MD, USA.
b US Naval Medical Research Unit-3, Cairo, Egypt.
c Biometry and Mathematical Statistics Branch, National Institute of Child Health and Human Development, Bethesda, MD, USA.

Reprint requests to: Abdollah B Naficy, Epidemiology Branch, National Institute of Child Health and Human Development, Room 7B03, 6100 Executive Boulevard, Rockville, MD 20852, USA.


    Abstract
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
Background To describe the seroepidemiology of Helicobacter pylori infection in a population of Egyptian children under 3 years.

Methods A cohort of children under 36 months, residing in Abu Homos, Egypt, were visited at home twice weekly. Information regarding the child's breastfeeding status was obtained, and periodic anthropometric and household hygiene surveys were performed. In June 1997, a serosurvey was conducted on 187 study participants over 6 months old. The serosurvey was repeated in October 1997. All sera were tested for IgG antibodies to H. pylori.

Results The June prevalence of H. pylori infection was 10%, and the incidence from June to October was 15%. Between June and October, 8 (42%) of 19 children that were positive for H. pylori infection seroreverted to negative. All seroreversions occurred in children 6–17 months. Other than age, no sociodemographic or environmental factor was significantly associated with incident H. pylori infection. There was no significant differences in the weight-for-age, weight-for-height, and height-for-age z-scores between children with and without prevalent H. pylori infection.

Conclusions Infection with H. pylori is common in Egyptian children under 3 years old and is not associated with malnutrition. No predictors for H. pylori infection were found. Our preliminary evidence for transient H. pylori infections in young children needs to be confirmed in a prospective cohort study, and predictors for persistent infection should be sought, since only these may be relevant to the known sequellae of infection.

Keywords Serology, incidence, prevalence, anthropometry, malnutrition, hygiene

Accepted 13 March 2000


    Introduction
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
There is strong evidence that infection with Helicobacter pylori causes chronic gastritis and peptic ulcer disease, and moderate evidence for a causal relation between H. pylori infection and gastric cancer.1,2 Furthermore, in Gambian infants and children, H. pylori infection has been associated with chronic diarrhoea and malnutrition.3,4 Although a causal relation could not be established, one study suggested that H. pylori infection preceded hypochlorhydria, which could be the mechanism leading to other enteric infections, recurrent diarrhoea, malnutrition, and growth failure.4

There are notable differences in the prevalence of H. pylori infection between developing and developed countries. In many developing countries, H. pylori infection begins in early childhood, with up to 50% of children being infected before the age of 10 years, and 80–90% of the population being infected by adulthood. In developed countries, infection rates are significantly lower with less than half of the population infected by adulthood.5,6

It was generally believed that following acquisition of H. pylori, and in the absence of treatment, infection would persist throughout life. However, based on seroepidemiological studies in adults and children from both developing and developed countries, it appears that the spontaneous elimination of H. pylori infection may occur.7

The mode of transmission of H. pylori is not definitively known, however, epidemiological studies suggest person-to-person transmission, by either faecal-oral or oral-oral routes, to be the major mechanism.8,9 In developing countries, there is evidence for both food- and water-borne transmission of H. pylori.10,11 The case for person-to-person transmission is supported by observations that factors such as lower socioeconomic status, lower levels of education, poorer hygiene and sanitation, and household crowding are associated with a higher prevalence of H. pylori infection.6 However, these associations are not inconsistent with food-borne transmission.

To date, there are no published population-based data on the childhood incidence of H. pylori infection in Egypt. This study was aimed to describe the seroepidemiology of H. pylori infection in a population of Egyptian infants and very young children. Our specific objectives were to determine age-specific prevalence and incidence rates of H. pylori infection, to identify sociodemographic and environmental factors associated with incident H. pylori infection, to determine the association between H. pylori infection and the occurrence of malnutrition, and to determine whether there was any evidence for the spontaneous elimination of H. pylori infection in this population.


    Methods
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
Study population
The study population consisted of children under 36 months residing in two rural villages in the vicinity of Abu Homos, located in the Nile Delta of Egypt. These children were participants in a cohort study designed to evaluate the aetiological role of enteric pathogens in this population. In January 1995 a house-to-house census of the study population was performed, during which baseline sociodemographic and household hygiene information was collected. Following the census, all children under 24 months and new births into the censused houses were eligible for enrolment into the cohort. Subjects enrolled in the cohort were observed until either they reached 36 months, they were lost to follow-up, or the study was concluded (February 1998). Prior to enrolment, written informed consent was obtained from each child's parent or guardian. The guidelines of the US Department of Health and Human Services and those of the authors' institutions for protection of human subjects were followed in the conduct of this study. Infants with major congenital abnormalities or severe chronic illnesses were not eligible for participation, however, all infants and children screened were found to be eligible for participation. During the study period, a total of 397 children were recruited into the study cohort.

Following enrolment, each child was visited at home twice weekly, during which time information regarding the child's diet and breastfeeding status was obtained. In addition, if the child was reported to have loose or watery stools, a faecal specimen was collected. Losses to follow-up recorded at the twice-weekly visits included 13 deaths and 10 out-migrations. At 3-month intervals, the study children were visited in their homes to obtain further information regarding their diet, and to determine their weight and height. Weights were measured to the nearest 0.1 kg using electronic Seca scales. Heights were measured to the nearest 0.1 cm using length boards. In children over 2 years, height sticks were used. Once every 6 months, a hygiene survey was performed for each study participant's household. All home visits and data collection were performed by social workers trained in study procedures.

Anthropometric data obtained in a survey performed on 7 June 1997 were used to evaluate the nutritional status of the children. The indices used to evaluate nutritional status were weight-for-age, weight-for-height, and height-for-age. The indices were standardized by calculating z-scores relative to growth reference curves developed by the National Center for Health Statistics using the Epinut software of Epi Info Version 6.03.12 Stunting and wasting were defined as z-scores of <–2 for height-for-age and weight-for-age, respectively. Severe stunting and wasting were defined as z-scores of <–3.

Serological surveys
During June and October 1997, blood samples were taken from all participants over 6 months old. In June 1997 blood was obtained from 187 (95%) of the 196 children surveyed. Of the 187 children bled in June, 173 (93%) were bled in October, 1997. Of the 14 children that were bled in June but not October, 12 had left the cohort by virtue of being over 36 months, and two had an insufficient amount of blood drawn. After collection, all blood samples were stored in iceboxes until transported later the same day to the field laboratory in Abu Homos. In the field laboratory, the serum was separated and stored at –20°C until transportation on dry ice to the Naval Medical Research Unit #3 laboratories in Cairo, Egypt, where the serum was tested for IgG antibodies to H. pylori.

Laboratory methods
All sera were tested for IgG antibodies to H. pylori with a commercially available enzyme immunoassay (HM-CAP; Enteric Products, Inc.), and according to instructions given by the manufacturer. ELISA values of <1.8 were considered negative, those >2.2 were considered positive, and those between 1.8 and 2.2 were considered indeterminate. Samples giving indeterminate results were re-tested, and those remaining indeterminate were considered negative. In a sample of US subjects (median age 44 years) the HM-CAP ELISA had a sensitivity of 98.4%, and a specificity of 96.4% for detecting H. pylori infection compared to the 13C-urea breath test.13 In a study that evaluated 169 serum samples from children 0–18 years old, 3 (1.8%) false positives and 1 (0.6%) false negative occurred when the HM-CAP ELISA was compared with an in-house EIA that had been validated using the 13C-urea breath test or gastric mucosal biopsy.14

Analyses
Prevalence rates of H. pylori infection were calculated by dividing the number of participants positive for H. pylori during the June serosurvey by the total number of participants in the same serosurvey. Incidence rates of H. pylori infection were calculated by dividing the number of participants who converted from negative to positive for H. pylori between the June and October serosurveys by the total number of participants negative for H. pylori during the June serosurvey. Seroreversion rates were calculated by dividing the number of participants who converted from positive to negative for H. pylori between the June and October serosurveys by the total number of participants positive for H. pylori during the June serosurvey.

The independent associations between variables under study and the incidence of H. pylori infection were estimated by multivariate analyses, using logistic regression models. Associations, expressed as odds ratios (OR), were derived from the model coefficients. The variables evaluated as potential predictors of H. pylori incidence were gender, crowding (number of people in household/number of rooms in house), presence of a household latrine, presence of a household garbage container, visible faeces in a household room (sleeping, eating, or cooking room), uncovered garbage in a household room (sleeping, eating, or cooking room), water source for drinking (municipal versus other), whether the house had electricity, maternal education (any versus none), and breastfeeding (any versus none). After adjusting for age, all exploratory variables with statistical significance of <=0.05 were included in the multivariate models. In all multivariate analyses, profile likelihood confidence intervals were computed, and statistical significance was defined as a P-value of <0.05 (two-tailed). To evaluate statistically significant differences in the weight-for-age, weight-for-height, and height-for-age z-scores between children who were infected with H. pylori and children who were not, linear regression models were used with adjustments made for potentially confounding variables.


    Results
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
In the cohort, the overall prevalence of H. pylori infection in June 1997 was 10%, with age-specific prevalence rates ranging from 5% to 15% (Table 1Go). Between June and October 1997, the overall incidence of H. pylori infection was 15%. There was a significant difference (P = 0.019) in age-specific incidence rates, which varied from 5% in the 24–29-month age group up to 33% in the 12–17 month age group (Table 2Go).


View this table:
[in this window]
[in a new window]
 
Table 1 Age-specific prevalence rates of Helicobacter pylori infection in June, 1997, Abu Homos, Egypt
 

View this table:
[in this window]
[in a new window]
 
Table 2 Age-specific incidence and seroreversion rates of Helicobacter pylori infection from June–October 1997, Abu Homos, Egypt
 
A high seroreversion rate was also noted among subjects in the younger age groups. Of the 11 children aged 6–17 months who had serological evidence of infection with H. pylori in June, 8 (73%) seroreverted to negative in October. However, no subject over 18 months old with serological evidence of H. pylori infection in June seroreverted by October (Table 2Go).

Other than age, no sociodemographic or environmental factor was found to have a statistically significant association with the incidence of H. pylori infection in the study population (Table 3Go).


View this table:
[in this window]
[in a new window]
 
Table 3 Crude and adjusted odds ratios (OR) for the associations between selected sociodemographic or environmental factors and the incidence of Helicobacter pylori infection between June and October 1997, Abu Homos, Egypt
 
A summary of the results of the anthropometry survey conducted in June 1997, is shown in Table 4Go. During this survey, anthropometry was performed on 184 of the 187 children who participated in the June serosurvey. Compared to the reference population, 18% and 11% of the study population surveyed had evidence of stunting and wasting, respectively. Severe stunting or wasting was observed in 10 (5%) and 2 (1%) of the 184 children surveyed, respectively.


View this table:
[in this window]
[in a new window]
 
Table 4 Summary of anthropometric survey conducted June 1997, Abu Homos, Egypt
 
The mean weight-for-age z-score was the same (–0.80) in both the H. pylori seropositive and the H. pylori seronegative subjects. The mean weight-for-height and height-for-age z-scores were –0.03 and –1.2 in the H. pylori seropositive subjects, and 0.04 and –1.3 in those seronegative, respectively. The differences in mean z-scores were not significant, and remained so after adjusting for age, maternal education, presence of a household latrine, or household crowding.


    Discussion
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
Our findings, similar to those obtained in other less-developed settings worldwide, demonstrate that infection with H. pylori is common in Egyptian children under 3 years. An interesting and important observation in our study was the apparent dynamic nature of H. pylori infection in infants and young children. During the 4-month period between the two serosurveys, we observed an incidence of 15% and a seroreversion rate of 42%. The eight children who seroreverted were under 18 months old. It has been shown that transplacentally transferred maternal anti-H. pylori IgG antibodies disappear by 6 months of age.15 Since only two seroreversions in our study occurred in children 6 months old, it is unlikely that the seroreversions can be explained solely by the loss of passively transferred maternal antibodies. Rather, our results suggest that in young Egyptian children, at least initially, infection with H. pylori may be a transient event. Recently, further evidence has been reported to support this hypothesis. In a cohort of Peruvian children who were followed for 2 years and serially administered 13C-urea breath tests to determine infection with H. pylori, prevalence rates were seen to decrease from 71% at 6 months old to 48% at 18 months old. Of the 56 children who completed all five scheduled breath tests during the 2-year study period, 37 had one or more negative tests after a positive test.16 In another study utilizing 13C-urea breath tests, prevalence rates of H. pylori infection in Nicaraguan children with persistent diarrhoea were seen to decrease from 91% in those under 12 months to 63% in those 13–65 months.17 Evidence that H. pylori infection may indeed be a reversible process has also been provided in several studies from developed countries,18–23 however, children under 3 years were evaluated in only one of these studies.19

We found no statistically significant associations between selected sociodemographic or environmental factors and the incidence of H. pylori infection. It is conceivable that we did not find significant associations for variables that have been associated with H. pylori infection in previous studies, such as crowding and lower socioeconomic status,6 because of the limited study sample size.

It has been demonstrated that acute infection with H. pylori can lead to hypochlorhydria, and so we postulated that H. pylori infection may predispose to diarrhoea and malnutrition. Although a study in Gambian children did find a positive association between H. pylori infection and chronic diarrhoea and malnutrition,3,4 no such association was found in another study conducted in Nicaraguan children.17 As in the latter study and another study conducted in Guatemalan children,24 we did not find any significant association between H. pylori infection and malnutrition.

Our results suggest that H. pylori infection is a dynamic process, even in the very young, and raises several important issues that need to be addressed in future studies. Since the currently known sequellae of H. pylori infection are believed to result from chronic infection, it will be important to differentiate between children who have transient H. pylori infections and those with persistent H. pylori infections. How should persistent infection be defined? If, in the absence of definitive therapy only some H. pylori infections persist, are there any socioeconomic, behavioural, or environmental predictors of persistent infection? Similarly, are there any predictors of the ability to clear an H. pylori infection before it becomes persistent? Does persistent infection predispose to other enteric infections, diarrhoea, or malnutrition? Finally, in this population of infants and young children, it will be essential not only to determine the sensitivity and specificity of a commercial ELISA compared with the 13C-urea breath test, but also to determine how each of these diagnostic tests perform with respect to transient or persistent H. pylori infections. We have begun a prospective cohort study of newborns in Abu Homos, Egypt, designed specifically to study the epidemiology of H. pylori infection, which we expect, once completed, to answer these important questions.


    Acknowledgments
 
The opinions and assertions contained herein are the private ones of the authors and are not to be construed as official or as reflecting the views of the Department of Defense or the Navy.

Financial support was provided by the Naval Medical Research and Development Command (Work Unit No. B6900101. PIX.3270), the National Institute of Child Health and Human Development (Interagency Agreement Y1-HD-7186–02), the World Health Organization Global Programme for Vaccines and Immunization, and the World Health Organization Control of Diarrheal Diseases Programme.


    References
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
1 Helicobacter pylori in peptic ulcer disease. NIH Consensus Statement 7–9 Feb 1994;12:1–22.

2 Veldhuyzen van Zanten SJ, Sherman PM. Helicobacter pylori infection as a cause of gastritis, duodenal ulcer, gastric cancer and nonulcer dyspepsia: a systematic overview. Can Med Assoc J 1994;150:177–85.[Abstract]

3 Sullivan PB, Thomas JE, Wight DGD et al. Helicobacter pylori in Gambian children with chronic diarrhea and malnutrition. Arch Dis Child 1990;65:189–91.[Abstract]

4 Dale A, Thomas JE, Darboe MK, Coward WA, Harding M, Weaver LT. Helicobacter pylori infection, gastric acid secretion, and infant growth. J Pediatr Gastroenterol Nutr 1998;26:393–97.[ISI][Medline]

5 Taylor DN, Blaser MJ. The epidemiology of Helicobacter pylori infection. Epidemiol Rev 1991;13:42–59.[ISI][Medline]

6 Bardhan PK. Epidemiological features of Helicobacter pylori infection in developing countries. Clin Infect Dis 1997;25:973–78.[ISI][Medline]

7 Xia HX, Talley NJ. Natural acquisition and spontaneous elimination of Helicobacter pylori infection: clinical implication. Am J Gastroenterol 1997;92:1780–87.[ISI][Medline]

8 Goodman JK, Correa P. The transmission of Helicobacter pylori: a critical review of the evidence. Int J Epidemiol 1995;24:875–87.[Abstract]

9 Mendall MA. Transmission of Helicobacter pylori. Semin Gastrointest Dis 1997;8:113–23.[Medline]

10 Hopkins RJ, Vial PA, Ferreccio C et al. Seroprevalence of Helicobacter pylori in Chile: vegetables may serve as one route of transmission. J Infect Dis 1993;168:222–2.[ISI][Medline]

11 Klein PD, Gastrointestinal Physiology Working Group, Graham DY, Gaillour A, Opekun AR, Smith EO. Water source as risk factor for Helicobacter pylori infection in Peruvian children. Lancet 1991;337: 1503–06.[ISI][Medline]

12 Dean AG, Dean JA, Coulombier D et al. Epi Info, Version 6: A Word-processing, Database, and Statistics Program for Public Health on IBM-compatible Microcomputers. Atlanta, GA: Centers for Disease Control and Prevention, 1995.

13 Marchildon PA, Ciota LM, Zamaniyan FZ, Peacock JS, Graham DY. Evaluation of three commercial enzyme immunoassays compared with the 13 C urea breath test for detection of Helicobacter pylori infection. J Clin Microbiol 1996;34:1147–52.[Abstract]

14 Sunnerstam B, Kjerstadius T, Jansson L, Giesecke J, Bergstrom M, Ejderhamn J. Detection of Helicobacter pylori antibodies in a pediatric population: comparison of three commercially available serological tests and one in-house enzyme immunoassay. J Clin Microbiol 1999;37: 3328–31.[Abstract/Free Full Text]

15 Gold BD, Khanna B, Huang LM, Lee C-Y, Banatvala N. Helicobacter pylori acquisition in infancy after decline of maternal passive immunity. Pediatr Res 1997;41:641–46.[Abstract]

16 Klein PD, Gilman RH, Leon-Barua R, Diaz F, Smith EO, Graham DY. The epidemiology of Helicobacter pylori in Peruvian children between 6 and 30 months of age. Am J Gastroenterol 1994;89:2196–200.[ISI][Medline]

17 Kehrt R, Becker M, Brosicke H, Kruger N, Helge H. Prevalence of Helicobacter pylori infection in Nicaraguan children with persistent diarrhea, diagnosed by the 13 C-urea breath test. J Pediatr Gastroenterol Nutr 1997;25:84–88.[ISI][Medline]

18 Ashorn M, Maki M, Hallstrom M et al. Helicobacter pylori infection in Finnish children and adolescents. A serologic cross-sectional and follow-up study. Scand J Gastroenterol 1995;30:876–79.[ISI][Medline]

19 Granstrom M, Tindberg Y, Blennow M. Seroepidemiology of Helicobacter pylori infection in a cohort of children monitored from 6 months to 11 years of age. J Clin Microbiol 1997;35:468–70.[Abstract]

20 Roosendaal R, Kuipers EJ, Buitenwerf J et al. Helicobacter pylori and the birth cohort effect: evidence of a continuous decrease of infection rates in childhood. Am J Gastroenterol 1997;92:1480–82.[ISI][Medline]

21 Kumagai T, Malaty HM, Graham DY et al. Acquisition versus loss of Helicobacter pylori infection in Japan: results from an 8-year birth cohort study. J Infect Dis 1998;178:717–21.[ISI][Medline]

22 Malaty HM, Graham DY, Wattigney WA, Srinivasan SR, Osato M, Berenson GS. Natural history of Helicobacter pylori infection in childhood: 12-year follow-up cohort study in a biracial community. Clin Infect Dis 1999;28:279–82.[ISI][Medline]

23 Redlinger T, O'Rourke K, Goodman KJ. Age distribution of Helicobacter pylori seroprevalence among young children in a United States/Mexico border community: evidence for transitory infection. Am J Epidemiol 1999;150:225–30.[Abstract]

24 Quinonez JM, Chew F, Torres O, Begue RE. Nutritional status of Helicobacter pylori-infected children in Guatemala as compared with uninfected peers. Am J Trop Med Hyg 1999;61:395–98.[Abstract/Free Full Text]