Around 77 percent of pasteurised milk samples assessed in a study were found to have high levels of bacteria, making direct consumption of such milk unsafe.

The level of bacteria found was beyond the standards set by Bangladesh Standards and Testing Institution, said the study.

“Raw or pasteurised milk available in the market are found to be contaminated with disease-causing organisms and should not be consumed without thorough boiling,” said Mohammad Aminul Islam, associate scientist and head of the Food Microbiology Laboratory at icddr,b.

Consuming such milk can cause various diseases like diarrhoea, dysentery and typhoid, he said.

“And, even if you drink the milk after boiling, nutrition value is heavily compromised,” said Aminul, principal investigator of the study conducted by icddr,b, with support from CARE Bangladesh.

The International Journal of Food Microbiology published the study on April 24.

To assess the microbiological quality of milk at different stages of the dairy value chain, scientists collected 438 raw milk samples from milk producers, collectors, chilling plants and restaurants in 18 upazilas of Bogra, Gaibandha, Nilphamari, Dinajpur, Joypurhat, Rangpur and Sirajganj.

Additionally, 95 samples were collected from commercially processed milk found on the shelves of retail stores in Dhaka and Bogra.

Scientists found that at the primary producers' level, 72 percent milk samples were contaminated with coliform and 57 percent were contaminated with faecal coliform bacteria. And, 11 percent of samples had high levels of E. coli.

The presence of faecal coliform bacteria in milk indicates that the milk has been contaminated with pathogens or disease-producing bacteria or viruses, the study said. 

Scientists found such high level of bacteria in pasteurised milk, though pasteurisation is done to kill pathogenic bacteria to make the milk safe for consumption.

Both national and international standards have zero tolerance for the faecal coliform bacteria in pasteurised milk.

The study says chilling-plant samples were found to be contaminated even at a higher rate than those taken from collection points. Samples collected from all 15 chilling plants in five districts were contaminated with coliform as well as faecal coliform.

Presence of some other bacteria such as B. cereus and staphylococci were also found in the samples but within the normal limit.

Asked how the milk is contaminated, Aminul told The Daily Star that dairy farmers' poor hygiene practices, environment and delayed in getting the milk to the chilling points from the farmers could be the factors.

“As there is some level of bacteria in milk, it multiplies when milk is kept in temperature ranging from 30 to 40 degrees Celsius,” he said.

Again, at the retail level, the bacteria can multiply if the milk is not in the refrigerator, he added.

The study suggested that Bangladesh's dairy companies ensure end-to-end compliance.

“Maintenance of seamless cold chain throughout the distribution channel of pasteurised milk from factory to consumer's table is critical for ensuring safe milk for consumption,” Aminul said.