Weekend Argus (Saturday Edition)
On a mission to fight listeriosis
10 Disease detectives hunt the source of ST6 outbreak following 61 deaths
THERE is a killer on the loose and Nevashan Govender is on its trail.
But the killer could be anywhere, and this is why Govender has had sleepless nights over the last couple of months. His quarry might be lurking on a vegetable farm, hiding in an abattoir or going unnoticed in a food processing plant.
The field epidemiologist is the head of the Emergency Operation Centre at the National Institute for Communicable Diseases, in Sandringham, Joburg.
He and his team co-ordinate the country’s response to any large epidemic outbreak, and for now they have their hands full hunting the source of ST6, a virulent strain of listeriosis that so far has killed 61 people.
“We are disease detectives,” he said describing himself and his team.
In recent months, the centre carefully monitored the bubonic plague outbreak in Madagascar and made sure it didn’t land on our shores.
But this adversary is different from the other disease outbreaks Govender has dealt with in the past.
The problem, listeriosis is so good at hiding. Most people who become infected with ST6, don’t even know they have the disease. They might come down with bout of diarrhoea or a fever and consider it nothing more than a stomach bug.
It is the elderly, newborns, pregnant women and people with weakened immunity who are at risk.
Listeriosis can kill through causing meningitis or septicaemia. Infections during pregnancy can lead to miscarriages, stillbirth or a life-threatening infection of the baby. The bacteria’s main path of infection is through contaminated food products.
The problem for epidemiologists is that the disease can occur weeks after eating contaminated food.
Prevention, like with many other diseases, comes down to following basic hygiene, washing vegetables, cooking raw food thoroughly and reheating leftovers.
It is from those patients who end up in hospital that Govender and his team hope to find the smoking gun that will lead them to the source of ST6.
At hospitals patients who are suspected to have listeriosis are tested. If the results come back positive, the institution is informed. Field epidemiologists then get in contact with the patient and interview them extensively.
Dr Katherine Calver is one of the epidemiologists tasked with interviewing listeriosis patients.
She has noticed that those infected with the disease seek medical attention at both public and private hospitals. It appears to not differentiate between rich and poor.
“You need to do it as soon as you can or people will forget their food history,” Calver says.
The patients she has spoken to have been willing to help as they want to know the cause of their illness.
“We try and find a pattern, but it is notoriously difficult because of the vast number of food items,” explains Govender. “We are not looking for a needle, we need to find the haystack.”
Ultimately CSI will play an important part in hunting down the source of ST6. Besides interviewing patients who have become infected with the disease, samples are sent to the NICD and are tested.
Samples are cultured and genetically sequenced to confirm it is ST6.
On a computer in one of the laboratories, ST6 cases are represented as purple dots on a map of South Africa.
A graph shows how the number of purple dots began to spike in the middle of last year. It was roundabout then doctors at the Steve Biko laboratories and at Chris Hani Baragwanath Hospital began noticing an increase in the number of cases of listeriosis.
“They said that they had seen a handful of listeriosis cases and that this is unusual and they asked if we could look into this,” says Govender.
“We have had flare-ups in the past but it has never been on this scale.”
The biggest cluster of purple is in Gauteng, which has made the investigators suspect the source of the disease is somewhere in the province. The Eureka moment in the search would be a food item contaminated with listeriosis that has the same genetic profile as those patients, represented with those purple dots. But so far this hasn’t happened.
“We just need more samples,” says medical scientist Shannon Smouse of the Centre for Enteric Disease.
Once ST6 has been flushed out, and the source identified, the plan is to have a closer look at the disease.
To genetically pick it apart and work out why it is so virulent. But that is in the future.
“Because we have such a large vulnerable population, the sooner we find the source the better,” said Govender.