Letter: Immune electron microscopy and hepatitis A

The reliability of the examination of foods, processed for safety, for enteric pathogens and Enterobacteriaceae: a mathematical and ecological study

Because of the paucity of quantitative data on numbers of other enteric pathogens in food, the reliability of the examination of processed foods for Enterobacteriaceae was estimated taking Salmonella as a model. For this purpose an assessment was carried out of the risk of accepting Salmonella contaminated consignments of foods, despite a negative outcome of (i) examination of 1.5 kg samples for Salmonella; (ii) examination of one or two 1 g samples for Enterobacteriaceae; (iii) simultaneous application of both tests. The computations were based on the results of the examination of 6830 samples of dried foods, processed for safety, out of a total of 18170 samples.Only 69 samples permitted the exact calculation of the epsilon-factor, defined as c.f.u./g of Enterobacteriaceae/c.f.u./g of Salmonella; 4642 were positive for the former group but ;free' from Salmonella, and the rest were negative in both tests. Numbers of c.f.u./g for both groups, and hence the epsilon-factors, varied widely between commodities and also between different consignments of the same food product. The average for epsilon amounted to 5.8 x 10(3), far from the base-line value of 0.75 x 10(3) assessed earlier. In only 0.1% of samples did the Enterobacteriaceae test fail to achieve the required consumer protection.This investigation therefore substantiates that testing foods processed for safety by examining accurately chosen quantities for ecologically well selected and taxonomically thoroughly defined index organisms is a most effective procedure in terms both of consumer protection and simplicity of examination without compelling the food industry to achieve hardly attainable microbiological quality standards.

Comparison of human fecal and serum parvo-like viruses

Parvovirus-like particles found in the sera of two blood donors had the size and appearance on electron microscopy of a virus (B19) found in the serum of a blood donor by Cossart et al. (1975), and those of a virus found in the feces of a normal subject. Antibody to these viruses was detected by immune electron microscopy and immunoelectro-osmophoresis in the sera of 50 children aged 10 to 15 years. Of these, 36% had antibody to the fecal virus, 36% had antibody to B19, and 54% had antibody to the two other serum viruses. The results of these tests suggest that serologically the three serum viruses were similar to one another, but that the fecal virus was distinct. The two blood donors had nonspecific symptoms at the time of viremia. Both donors had developed immunoglobulin M antibody to the virus when tested 3.5 and 4.5 weeks later, but no viruses were detected in the feces or urine.

Faecal shedding of hepatitis-A antigen

Serial stool specimens from two individuals with experimental hepatitis-A infection were examined and the shedding pattern of hepatitis-A antigen (HAAg) was determined by immune electron microscopy. HAAg particles were detected at least 5 days before the development of abnormal transaminase levels and jaundice, but not later than the day of peak transaminase levels. The pattern of early faecal shedding of HAAg particles correlated well with the early infectivity of faeces and accorded with the suggestion that HAAg is involved in the aetiology of hepatitis-A infection.