Helicobacter pylori infection in an Australian regional city: prevalence and risk factors

Abstract

MJA 1997; 167: 310-313  

Introduction

In developed countries, including Australia, the prevalence of H. pylori infection increases with age at the rate of about 1% per annum, to reach 40% or more at age 60 years.² In contrast, in developing countries prevalence is 40% or more at age 10 years.² Seroconversion in childhood also seems more likely in particular populations in developed countries; it was found to occur among people of lower socioeconomic background in Northern Ireland³ and England ⁴ and in a rural town in Western Australia.⁵

Suspected childhood risk factors for H. pylori infection in developed countries include having a single parent, lower parental social class, greater housing density or proportion of rented housing in school catchment area, overcrowding, bed-sharing, and absence of a fixed hot water supply.⁶ In adults, previously investigated risk factors include race-ethnicity, socioeconomic status, education, dental prosthesis and irregular dental treatment, public contact, working with animals, smoking status, alcohol consumption, homosexuality, sexually transmitted diseases, and having an infected child or partner.^1,2,7-10

To assess the importance of these and other risk factors for H. pylori infection in Australia, we investigated the H. pylori status and risk factors of a sample of adults in Ballarat, a regional city in Victoria.  

Methods

Setting and population

The study was approved by the Ballarat Base Hospital Ethics Committee.  

Investigations

Statistical analyses

Odds ratios (ORs) and 95% confidence intervals (CIs) for suspected risk factors for H. pylori infection were produced by logistic regression analyses. Collinearity was first assessed through a series of multiple linear regression analyses, using each predictor variable in turn as the dependent variable and all others as independent variables. Dependent variables with an R² greater than 0.95 were excluded. All remaining variables were entered into the logistic regression model, and then excluded manually in a stepwise manner if they were not significantly associated with H. pylori status and had an OR in the range 0.95-1.05. Edentate subjects were assigned the mean plaque score of subjects with teeth, as recommended by Thompson.¹⁷ This avoided having to analyse edentate and dentate subjects separately, with the inevitable loss in precision when estimating risk associated with other variables.

The effect of response to the study on ORs was assessed by the method of Criqui.¹⁸ The associations found using H. pylori status as a dichotomous variable, based on a cut-off antibody titre of 500, were confirmed using H. pylori antibody titres (logarithmically transformed) as a continuous variable in a multiple linear regression model.  

Results

The association between positive H. pylori antibody status and possible risk factors in the final logistic regression model is shown in the Box. In the final model, which adjusted for age, sex and socioeconomic index of residence, the following were significantly associated with positive H. pylori status: increasing number of buccal and lingual tooth surfaces with a plaque score ≥2 (adjusting for the absence of natural teeth and number of teeth), increasing years in a job with public contact, presence of blood group B antigen, and having lived in a household of six or more people during the first 16 years of life. Washing of hands only sometimes or rarely after using the toilet and visiting a dentist less than once a year had a large but not statistically significant association with positive H. pylori status.

Negative H. pylori status was significantly associated with increasing education, having ever lived on a farm, and having teeth scaled less than once a year. Univariate analysis showed that dentate subjects who visited a dentist at least annually had a significantly lower prevalence of H. pylori infection if they had their teeth scaled less than once a year (three out of 25) compared with more often (20 out of 56) (chi-squared = 4.78; P = 0.03; 1 degree of freedom). In addition, among those who had their teeth scaled less than once a year, visiting a dentist at least annually was protective (three infected out of 25) compared with visiting a dentist less often (27 infected out of 78) (chi-squared = 4.69; P = 0.03; 1 degree of freedom).

The following variables were initially included in the logistic regression model, but excluded from the final model because of lack of a significant association with H. pylori status: dentures, history of gum infections, frequency of sharing toothbrush or cup, travel to high prevalence countries, smoking status, lifetime alcohol consumption, vegetarian diet, eating unwashed home-grown vegetables, washing hands before eating, years with occupational or recreational contact with animals, having visited farms, marital status, height, weight, and variation between interviewer/oral health observers.

The results of multiple regression analysis confirmed those of the logistic regression analysis for all variables except increasing education, which was negatively, but not significantly, associated with H. pylori titre.  

Discussion

The cost-benefit ratio for eradicating H. pylori infection with antibiotics in asymptomatic adults will not be known for some time.²⁰ It is therefore important to identify factors associated with the acquisition and transmission of H. pylori. This is the first time that

• Public contact through employment;
• Moderate or heavy accumulation of dental plaque;
• Frequent scaling of teeth;
• Only rarely or sometimes washing hands after using the toilet; and
• Having blood group B antigen

The association between H. pylori infection and public contact through employment was not surprising, as overcrowding in childhood has led to speculation that close personal contact may promote transmission of the organism.⁷ The protective effect of having lived on a farm in our study may be a consequence of low population density in rural areas. Rural China has a significantly lower prevalence of H. pylori infection, despite poorer standards of hygiene, compared with urban China.^2,21

There is other evidence to corroborate our finding that moderate or heavy accumulation of dental plaque is significantly associated with H. pylori infection. H. pylori has been cultured from dental plaque, and identical H. pylori ribotypes were found in the mouth and gastric antrum of ulcer patients.^22,23 Moreover, H. pylori has been detected by reverse transcription polymerase chain reaction in only moderate to heavy accumulations of plaque.²²

Our finding that visiting the dentist less than once a year increased the risk of H. pylori infection is consistent with the protective effect of regular dental treatment found by Gasbarrini et al.¹⁰ If H. pylori inhabits plaque, scaling may lead to ingestion of the organism and inoculation of the stomach. A decreased risk of H. pylori infection from having teeth scaled less than once a year is therefore plausible.

In agreement with other studies, we found no significant association between H. pylori infection and alcohol consumption. We also found no significant association with smoking, although 52% of our sample were current or ex-smokers. Others have found significantly more smokers among patients with no abnormalities on endoscopy who had H. pylori infection,⁸ and the difference could be caused by confounding by oral hygiene. Smokers have poor oral hygiene and visit their dentist and brush their teeth less often than non-smokers.²⁴ Further, in our study, dentate subjects who had ever smoked had a significantly larger mean number of tooth surfaces with a high plaque score than non-smokers, after adjusting for number of teeth (P = 0.02).

Although the risk of H. pylori infection was increased for people who washed their hands only sometimes or never after using the toilet, because of the small number of these subjects the odds ratio had a wide confidence interval and the association was not significant. Faecal-oral spread of the organism is known to occur, but our data imply that it is relatively uncommon between adults, as others have suggested.¹ Nevertheless, this result underlines the importance of good hygiene practices and the provision of handwashing facilities both indoors and out-of-doors. Eating from communal bowls has been postulated as a mechanism of H. pylori transmission in China.²¹ Our study found that sharing of cups and cooking utensils was not common in Ballarat and not a risk factor.

Genetic effects have been found to influence the acquisition of H. pylori.¹ However, the importance of the association we found between the presence of blood group B antigen and H. pylori infection must await further research into the mechanisms of genetic susceptibility to H. pylori infection.

Our results imply that good hygiene practices are essential for those in frequent contact with the public to prevent H. pylori transmission. As moderate to heavy dental plaque emerged as a clear risk factor, reducing plaque may have an important role in preventing acquisition of H. pylori. This is another reason for educating the public, adults and children about effective tooth-brushing and other oral hygiene techniques. Regular dental treatment may need to be encouraged, while avoiding the ingestion of plaque debris which could occur during tooth scaling. In view of these potentially important public health implications, confirmatory evidence of our results should be sought.  

Acknowledgements

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