Editor,—We read with interest the article by Kerret al. While the proportion of samples positive for H pylori DNA were significantly higher in the SIDS group compared with the control group, the findings need to be interpreted with caution.

PCR is a useful tool for detection of DNA. It is, however, evidence that the DNA of the organism is present, not evidence that the organisms were alive or caused disease. Culture, microscopy, serological evidence or histological evidence of inflammatory or immune responses are needed to support the hypothesis that the bacteria were involved with pathological processes, not just transient contamination of the infant with DNA from non-viable bacteria.

There are several points that detract from the paper:

In relation to the findings reported:

1.

Only the PCR assays provided positive evidence. In contrast to other studies reported as abstracts, microscopic examination of the stained sections did not find any evidence of H pylori. This discrepancy needs to be explained. There were no serological data to support the PCR findings and no data from histological examinations to provide evidence that the bacteria were causing infection or that inflammatory responses had been elicited.

2.

The proportion of PCR positive samples among SIDS infants (88%) was significantly larger than that among controls (12.5%). The possibility of contamination was not addressed for SIDS or the positive control case. There was no demonstration by molecular methods that the DNA detected was from different strains. H pylori strains show great genetic variability and previous studies demonstrated that most individuals carry unique strains. Isolates from different individuals that appear to be genetically identical are those obtained only from close contacts, usually within a family.

 The interpretation of the epidemiological data forH pylori and socioeconomic factors was not assessed in …