Extra Credit, H. Pylori

Research

Gastroenteritis and Transmission of Helicobacter pylori Infection in households

Sharon Perry, Maria de la Luz Sanchez, Shufang Yang, Thomas D. Haggerty, Phillip Hurst, Guillermo Perez-Perez, and Julie Parsonnet

Stanford University School of Medicine, Stanford, California, USA; Santa Clara County Health and Hospital Systems, San Jose, California, USA; and New York University of Medicine, New York, New York, USA

Abstract

The mode of transmission of Helicobacter pylori infection is not yet defined. In Northern California, 2,752 people-household members were tested for H. pylori infection in serum or stool. They were tested at a baseline visit and again three months later at a follow-up visit. At baseline visit 1,752 persons were diagnosed negative; at the follow-up visit, there were 30 new incidences of infection. Children age two and above accounted for 21% of these incidences. Exposure to an infected household member was associated with a 4.8-fold increased risk for definite or probable new infection. It was noted that if the infected household member had vomiting as a symptom the incidence of exposure increased as compared to members who have diarrhea only.

Helicobacter pylori infects at least 50% of the world's population. Infection occurs early in life. However, the precise age of inoculation is unknown. It often goes undetected. In industrialized countries, infection rates are declining rapidly, but high rates of infection persist among disadvantaged and immigrant populations.

The mechanisms of transmission of H. pylori are still not defined. The most common theory is person-to-person transmission by fecal/oral, oral/oral, or gastric/oral pathways. Infection is associated with crowding, poor hygiene, and intrafamilial clustering. This organism is reliably collected from vomit and stools during rapid gastrointestinal transit. These findings lead to the hypothesis that gastroenteritis episodes provide the opportunity for H. pylori transmission.

Household transmission of gastroenteritis is common in the United States, especially in households with small children. It is suspected that rates of new infection will be elevated after exposure to persons with H. pylori-infected cases of gastroenteritits. To determine if diarrhea or vomiting contribute to H. pylori transmission, households in California experiencing gastroenteritis were monitored and evaluated for infection of H. pylori. Symptoms of new infection were also monitored and noted.

The study population consisted of households that were participation in the Stanford Infection and Family Transmission study, initiated in1999 to prospectively evaluate the association of H. pylori infection and household gastroenteritis. Demographically, Hispanic immigrant families residing in South San Francisco Bay, has a high seroprevalence of H. pylori infection. Volunteers were selected from near-by community clinics, who complained of diarrhea, vomiting or both. Visits were made to the volunteers homes, they were interviewed regarding symptoms, onset, and duration of gastroenteritis within the previous 21 days. Both stool and blood samples were taken to test for H. pylori.

Stool samples were collected from children and others who refused to have their blood drawn. Approximately three weeks later the same people were re-visited, re-interviewed and another sample taken for testing. Volunteers were given a gift for their participation.

Laboratory Methods

H. pylori Serologic Testing

Anti-H. pylori immunoglobulin G (IgG) was quantified by using an in-house ELISA. Optical density (OD) results were categorized as negative, borderline, or positive. This test is 91% sensitive and 98% specific for infection in adults. Serologic testing in children was considered unreliable for this study.

Each sample was tested three times on two separate occasions; first soon after the sample was received and later, when it was paired with the second visit sample from the same study participant. Between testing the samples were frozen at -80˚ C. The paired serum results are presented here. High reproductivity between first and second runs of the same sample suggests that the effect of freezing or storage was negligible. Titer levels were derived from ODs by standard curve methods. A seroconversion was defined as a qualitative change from negative to positive, negative to borderline, or borderline to positive, if accompanied by ≥4-fold increase in H. pylori titer from baseline. A seroreversion was defined as a qualitative change from positive to negative, accompanied by ≥2-fold decrease in H. pylori titer.

To corroborate recent H. pylori infection, serum samples from 22IgG seroconverters and 22 randomly sampled, persistently seronegative adults were tested for H. pylori IgM antibody response in the laboratory of Dr Perez-Perez by using a mixed strain assay previously validated in ethnically diverse and pediatric populations. Detection of an IgM antibody response at either first or 12-week follow-up visit was considered a positive test result.

H. pylori Stool Antigen

Stool antigen was tested with the Premier Platinum HpSA enzyme immunoassay. Stool samples collected at home visits were transported to the laboratory and stored at -20˚ C until processed. Samples not available at home visit were expressed by overnight mail. In one metaanalysis, stool antigen had a mean sensitivity and specificity of 91% and 93% respectively; however, accuracy may be lower in children less than six years of age. In the present study population, H. pylori was identified by PCR in 12 of 26 transiently positive stool samples from toddlers, a finding that was consistent

with the 50% sensitivity of PCR observed in H. pylori-inoculated stools. A stool conversion was defined as a qualitative change from negative to positive when the manufacturer's suggested cut-off values were used.

Testing Protocol

They requested stool and serum from all volunteers age two and older, although participants were included in the study if they offered one or the other. For practical reasons (stool samples are not always available on demand, and they are unpleasant to ship) most people only provided blood samples. Approximately 29% of children over two years of age provided only blood samples and 89% provided both blood and stool samples.

Definitions