Investigation of a suspected Foodborne outbreak at a village in Leribe District, Lesotho, September 2021

Mahloli Ratsiu^{1,2, &}, Mahlape Tiiti², Hellen Kgatla¹, Tsepang Lekhela², Khuliso Ravhuhali¹

 

¹South African Field Epidemiology Training Programme (SAFETP), National Institute for Communicable Diseases, Johannesburg, South Africa, ²Disease Control Unit, Ministry of Health, Maseru, Lesotho

 

 

^&Corresponding author
Mahloli Ratsiu, South African Field Epidemiology Training Programme (SAFETP), 1 Modderfontein Road, Johannesburg, South Africa.

 

 

 

 

Foodborne diseases are caused by the contamination of food and occur at any stage of food production, delivery, and consumption field [1-3]. Globally, over 200 diseases are caused by eating food contaminated with bacteria, viruses, parasites, or chemical substances such as heavy metals [4]. Out of 600 million people who get sick after eating contaminated food, 420,000 die globally [5]. In Africa, an estimated 91 million people get ill from contaminated food, and 137,000 people die from these contaminated foods annually [6].

 

Food poisoning caused by pesticides may emanate from the ingestion of residues. Consumed pesticides may result in acute or chronic poisoning in humans. Food products can become contaminated with pesticides during storage, transportation, or handling processes. Arsenic compounds are classes of pesticides that are used as ingredients in rodenticides and rat poisons. Pesticide poisoning can result in a range of symptoms, including nausea, vomiting, diarrhoea, abdominal pain, dizziness, headaches, and in severe cases, respiratory distress, seizures, or even death [1, 5].

 

Zoonotic outbreaks are usually difficult to control due to difficulty identifying the nature of the sources of contamination [2,7]. The contamination could be from the environment or human-related animal handling practices. Transmission is usually through consuming contaminated animal products or direct contact with the infected animal. The animals may be contaminated with microorganisms, chemicals, or toxins [1, 8].

 

On Wednesday 8 September 2021, an epidemiologist was alerted of a rumour about people who got ill after consuming pork in Leribe District in Lesotho on a social media news page. Upon further inquiry, the District Medical Officer (DMO) confirmed the rumour, and the rapid response team initiated further investigations on 10 September 2021. The investigation was conducted to determine the causative agent, the source, and the extent of the outbreak and to recommend prevention and control measures.

 

 

Outbreak setting

 

The outbreak investigation occurred at a rural farming village in Leribe District, in the northern region of Lesotho. The community's most common farming practices are poultry, grain, and livestock farming. The community has access to health care services, water supply, and transport. The village population projections are estimated to be 284 [9].

 

Investigation design

 

A case series study design was used to conduct a thorough and detailed examination in order to characterise the cases involved in the outbreak.

 

Outbreak case definition

 

Suspected case: Any person presenting with acute diarrhoea with or without blood, seizures, nausea, vomiting, feeling feverish, dizziness, and/ or abdominal pain, burning sensation in the eyes, confusion with or without convulsions, frothing, decreased level of consciousness/ unconsciousness, who resided at a village in Leribe district in Lesotho from 6 – 10 September 2021.

 

Data collection

 

To identify cases, we reviewed medical records at a health facility. Case investigation forms (CIF) developed by the Ministry of Health were used to gather case information. Key informant interviews were conducted with the village chief, one health care worker, one village health care worker, and four community members to obtain information on possible exposures. The key informants assisted in filling the CIF for case A. The key informants were all persons who attended to the scene.

 

The composition of the rapid response team was composed of a field epidemiology resident, health inspector, surveillance officer, and animal laboratory scientist.

 

Environmental investigation

 

We conducted a direct inspection of the premises, including the pigs' kraal. We used the inspection tool from the Department of Environmental Health to conduct the assessment, which included food handling and preparation methods and environmental conditions.

 

Laboratory investigation

 

The clinician who attended to the cases at the hospital upon admission drew blood from two suspected cases to obtain a full blood count (FBC) and conduct Liver function tests (LFTs) and sent to the laboratory around 16h40 minutes on 6 September 2021. The results were received from the laboratory on 6 September 2021 around 17h00 minutes. The blood was drawn from cases with history of diabetes. We exhumed the dead pig and the dog to obtain their brains for rabies and anthrax testing at the National Laboratory of Lesotho. The dog was found dead at the scene on 7 September 2021 and was suspected to have eaten the remains of the dead pig. The liver samples from both the pig and dog were further exported to the Agricultural Research Council (ARC) in South Africa for toxicology testing.

 

Data analysis

 

We summarised data using Microsoft Excel and presented it using tables and graphs.

 

Ethical consideration

 

This situation constituted a public health emergency that necessitated an urgent and immediate response. Given the time-sensitive nature of the investigation and the need for rapid action to mitigate potential harm, it was not feasible to adhere to the standard ethical review process. Instead, a streamlined and expedited review process was implemented, prioritizing the protection of public health and safety while ensuring compliance with applicable ethical guidelines for emergency response scenarios. Permission to investigate the suspected outbreak was granted by the Ministry of Health. The objectives of the investigations were also explained to the participants and their verbal consent was obtained.

 

 

Epidemiologic characteristics of the cases

 

On the morning of 5 September 2021, the pigs caretaker discovered that one of the pigs was missing when she went to feed them. Quickly alerting the owner, they mobilised neighbours to aid in the search. Just the day before, the pig had appeared well.

 

After a thorough search, the pig was found, but it appeared weak with a lack of coordination accompanied by involuntary shaking of the body. Upon observation, there were no visible injuries on the pig. The pig was slaughtered, but due to the lateness of the hour, the owner opted not to disembowel the pig and stored it at room temperature overnight.

 

The next morning, the owner, along with four other men and the caretaker woman, commenced the disembowelling process. They cleaned the pork liver, which, upon inspection by the pig caretaker, appeared slightly yellowish with unusual smell. The pig caretaker fried the liver for approximately 10 minutes. Soon after consuming the liver with pap (mealie-meal porridge), they started feeling dizzy, feverish, burning eyes sensation, and diarrhoea. Realizing the severity of the situation, they sought help from neighbours (Figure 1).

 

Case-Patient A: This was a 43-year-old male presented with seizures, dizziness, abdominal pain, burning sensation in the eyes, confusion with convulsions, frothing, unconsciousness, and headache. He died at the scene before seeking medical attention at 10h30 minutes on 6 September 2021. No tests were performed on the deceased. Medical records showed that the patient was immunocompromised and was on antiretroviral treatment (ART).

 

Case-Patient B: This was a 62-year-old male who was the pig owner. Following consumption of the liver, he presented with abdominal pain, dizziness, headache, and loss of consciousness. He was administered cooking oil and activated charcoal by the neighbours and started presenting with diarrhoea and vomiting. He was taken to Hospital Z on 6 September 2021, where he was admitted overnight. Clinical examinations performed for case-patient B included blood pressure (132/68mmHg). No laboratory tests were performed. He was managed with metronidazole 500mg TDS. The patient was discharged the next day with BP (110/53mmHg).

 

Case-Patient C: This was a 48-year-old male; the pig owner's brother. Following the consumption of the liver, he presented with abdominal pain. He then presented with diarrhoea following administration of cooking oil and activated charcoal. He was taken to Hospital Z on 6 September 2021 where he was admitted overnight. Tests and clinical examinations performed for case-patient C included: random blood sugar (4.3mmol/L: ranges 3.9-5.6 mmol/L) and blood pressure (139/79mmHg). No laboratory tests were performed. He was managed with metronidazole 500mg TDS. He complained of mouth dryness the next day, but he had recovered.

 

Case-Patient D: This was a 69-year-old female who was the pigs' caretaker. She presented with abdominal pain, feverish, nausea, dizziness, and headache. She given activated charcoal by the neighbours leading to vomiting afterwards. She was taken to Hospital Z on 6 September 2021, where she was admitted overnight. Tests and clinical examinations performed for case-patient D included random blood sugar (7.5mmol/L: ranges 3.9-5.6 mmol/L), and blood pressure (120/58mmHg), AST (36 IU/l: ranges 0-31 IU/l), Neutrophils (9.20 *10^9/l: ranges 0.96-6.40 *10^9/l), Monocytes (1.11 *10^9/l: ranges 0.08-0.06 *10^9/l), Leucocyte count (11.8 *10^9/l: ranges 3.6-9.6*10^9/l). She was managed with Vitamin B Complex, alternate with 5% dextrose, 2g Ceftriaxone IV stat, HCTZ 25mg, and Metronidazole 500mg IV. The patient had recovered the next day and was discharged with BP (105/64mmHg).

 

Case-Patient E: This was a 58-year-old male presented with abdominal pain, nausea, dizziness, and headache. He was administered cooking oil and activated charcoal by the neighbours. He then presented with diarrhoea and vomiting. He was taken to Hospital Z on 6 September 2021, where he was admitted overnight. Tests and clinical examinations performed for case-patient E included: random blood sugar (7.5mmol/L: ranges 3.9-5.6 mmol/L), and blood pressure (120/58mmHg). Haematocrit (41.3%: ranges 48.0-52.0%), RDW (10.5%: ranges 11.0-14.0%). He was managed with Vitamin B Complex, alternate with 5% dextrose, 2g Ceftriaxone IV stat, and Metronidazole 500mg IV. The patient was discharged the next day with BP (132/62mmHg). On the morning of the 12 of September 2021, patient E presented with abdominal pain, dizziness, and headache. He went to the hospital to seek medical attention. He was treated and given medication to use at home.

 

Case-Patient F: This was a 47-year-old male presented with abdominal pain, dizziness, and headache. He was administered cooking oil and activated charcoal by the neighbours. He was taken to Hospital Z, where he was admitted. Clinical examinations performed for case-patient F included blood pressure (115/62mmHg). He was managed with metronidazole 500mg TDS. The patient was discharged the next day with BP (122/71mmHg).

 

Environmental Findings

 

In addition to human cases, on the 7th of September 2021, a piglet from the same household and two dogs were discovered dead. The rest of the pig's carcass was buried in the household's yard together with the piglet and the two dogs. The pigs' kraal was clean and well-maintained. There were eight pigs, including the dead pig, and the kraal is partitioned so that they live in pairs. They are fed formulated commercial pig foods. The other seven pigs were still in good health

 

There was no evidence of recent agricultural chemical use in the garden and the fields. Following the winter season, the fields were bare and without vegetation, and the villagers were preparing for summer ploughing. The interviewed villagers reported not having bought agricultural products such as seeds, fertilisers, herbicides, and pesticides yet because most of them are currently unavailable at the suppliers.

 

The villagers reported not having used any toxic household chemicals, such as rodenticides, recently, as they usually use cats for that purpose. The surroundings were generally well-kept, and there was no evidence of littering or unsafe disposal of household nuisances during the inspections.

 

Laboratory Findings

 

The pig brain tested negative for both anthrax and rabies. The toxicology results were received on the 21st September 2021 and were positive for arsenic poisoning.

 

 

This foodborne outbreak involved six cases and was associated with consumption of pig liver contaminated with arsenic. However, we did not identify the source of the arsenic poisoning. No similar outbreaks caused by arsenic poisoning in Lesotho have been reported. However, in other countries including Asia, arsenic poisoning has been reported. The source of arsenic has been found to be ground water.

 

Some pesticides are more toxic than others, and exposure to particular types, such as organophosphates or organochlorines, can lead to acute poisoning symptoms if ingested in high amounts. Due to their toxic effects on rodents, arsenic compounds have been used as ingredients in rodenticides and rat poisons. Arsenic-based pesticides have been banned in different countries including Lesotho due to their toxic effects on both human, animal and environment [5]. This ban is crucial in preventing poisoning and contamination in agricultural practices [5]. Our investigation did not find any evidence of arsenic containing products in the affected community.

 

Symptoms of arsenic poisoning may present with vomiting, dizziness, headache, fever, and confusion. Severe poisoning may be fatal [5]. In this outbreak, one case died, and five cases were symptomatic. The symptoms were consistent with arsenic poisoning. The severity and outcome of arsenic poisoning depend on the immunity of the patient [10]. During this investigation, Case A died at the scene, which might be explained by the compromised immunity of the patient.

 

Activated charcoal also works as an adjunctive therapy in treating food poisoning; it prevents biphasic and anaphylaxis reactions [11]. The deceased did not get the chance to drink activated charcoal which may have contributed his demise. In the five surviving cases of the foodborne outbreak, the appropriateness of the treatments offered can be evaluated based on standard recommendations for such outbreaks. The use of cooking oil, for example, would not typically be indicated as a treatment for foodborne illnesses unless it was specifically part of a culturally relevant or symptom-based remedy, such as soothing gastrointestinal discomfort. Antibiotic use should generally be reserved for specific bacterial infections, such as those caused by Salmonella or Shigella, but not for viral or toxin-mediated illnesses like those caused by norovirus or certain strains of E. coli, where antibiotics can exacerbate the condition. Ideally, supportive care like rehydration therapy, electrolytes, and, in severe cases, intravenous fluids should be prioritized, with antibiotics being prescribed only when there is clear evidence of a bacterial infection that requires such intervention [1, 5].

 

Appropriate slaughtering practices of the pig were not observed. The pig was killed on the 5th of September, and it was kept at room temperature overnight before it was disembowelled on 6 September 2021. Improper animal slaughtering often leads to bacterial accumulation, which may be toxic to human consumption. There is a possibility of arsenic and/or accumulation of bacteria in the carcass or severe reaction to the pork liver as causative agents for the outbreak poisoning. Severe arsenic poisoning may lead to convulsions, respiratory muscle paralysis, and gastrointestinal symptoms, including cramps, nausea, vomiting, and diarrhoea [10].

 

The outbreak is regarded as severe based on one case fatality and the hospitalisation of all the other cases. High white blood cell count (leucocytosis) can indicate a range of conditions including infections, inflammation, bodily injury, and immune system disorders [12]. Elevated percentage of neutrophils in the blood is called neutrophilia. Neutrophilia occurs when there is an infection in the body, most likely a bacterial infection. A high monocyte count (monocytosis) can happen when you are recovering from an acute infection. Elevated aspartate aminotransferase (AST) level is a sign of liver damage. It can also mean damage to another organ, like the heart or kidneys.

 

The coordination and collaboration of a multisectoral team during a foodborne outbreak exemplifies best practice recommendations for One Health and multisectoral outbreak investigations by fostering a comprehensive, integrated response [2, 5]. In line with One Health principles, such collaboration ensures the inclusion of diverse expertise, including human health, animal health, environmental health, and food safety sectors, to address all potential sources and vectors of infection. This cross-disciplinary approach enhances the detection, investigation, and control of outbreaks, while enabling more effective risk assessment, data sharing, and resource mobilization, ultimately leading to faster and more coordinated interventions and improved public health outcomes [1, 5].

 

The Rapid Response Team (RRT) investigated on 10 September, four days after the incident. The delay emanated from inactive RRT in the district. A robust RRT needs to be activated with clear terms of references to ensure real time reporting and activation of investigations. The delay in reporting may have introduced recall bias about the time of onset of symptoms [1, 5]. Stool and vomit samples for microscopy, culture and antimicrobial sensitivity testing were not collected to identify the cause of the outbreak. Postmortem was not performed to provide conclusive results. Toxicology was not performed on human samples due to limited laboratory capacity in the country. Pap (mealie-meal porridge) was not sampled to rule out if it was contaminated [1, 5].

 

 

Six people were affected by the outbreak following the consumption of pork liver. The outcomes of the outbreak were hospitalization of the cases and one fatality. Toxicology results were positive for Arsenic poisoning. Consumption of a pork liver positive for arsenic may have caused the outbreak. The primary source of arsenic remains unknown. Blood and urine samples should be collected for toxicology when one presents with food poisoning. There should be laboratory capacity building for different infections.

 

 

The authors declare no competing interests.

 

 

All authors contributed substantially to the write-up and review of the manuscript. MR, MT conducted the investigation. MR drafted and revised the manuscript. HM, TL, and KR participated in the supervision of the outbreak investigation and reviewed the draft manuscript. All authors reviewed and approved the final manuscript. The authors supervised and provided technical guidance in the follow-up of the cases. All authors reviewed and approved the final manuscript.

 

 

We acknowledge the South African Field Epidemiology Training Program (SAFETP), for their technical support and for facilitating the testing of samples through the Agriculture Research Council-Onderstepoort, South Africa. We also acknowledge ARC-Onderstepoort Veterinary Institute for their assistance in toxicology testing. We acknowledge the Ministry of Health Surveillance team for their guidance, and technical support. Motebang Hospital Surveillance team for joining the investigating team

 

 

Figure 1: Timeline of events of a suspected foodborne outbreak at a village in Leribe District, Lesotho - September 2021

 

 

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