A case of concomitant Plasmodium falciparum malaria and Bacillus cereus bacteremia in a traveler returning from Tanzania

Malaria has been associated with bacterial coinfections, but the importance of bacterial coinfections in uncomplicated malaria is poorly described. We present a unique case of a 27-year-old woman with concomitant Plasmodium falciparum and Bacillus cereus bacteremia who acquired these infections while traveling in Tanzania but became ill only after returning to the United States. Analysis of blood parasites revealed Plasmodium falciparum and blood cultures obtained at presentation showed Bacillus cereus. Even after completing malaria treatment, she continued to have abdominal pain and watery diarrhea, which improved only after intravenous vancomycin. Cases of Bacillus cereus bacteremia are reported in travelers and immigrants returning from countries where malaria transmission occurs, mainly from sub-Saharan Africa, but coinfection with Plasmodium falciparum and Bacillus cereus has not yet been described in the literature. In this case, malaria symptoms resolved after initiation of targeted treatment, but persistent diarrhea improved only after adequate anti-Bacillus cereus therapy. Persistent watery diarrhea and dehydration in patients with malaria should raise concerns about Bacillus cereus coinfection.


Malaria has been associated with bacterial coinfections and, in particular, with bacteremia. [1]. The bacteria most commonly isolated from the blood of malaria patients are non-typhoidal Salmonella species and other Gram-negative bacteria. [2]. In uncomplicated malaria, the importance of bacterial coinfections is poorly understood and the symptoms of malaria and bacterial infections may be similar.

In people with malaria, intestinal translocation of bacteria and increased erythrophagocytosis have been suggested as possible mechanisms for increased susceptibility to bacteremia. [3]. Malaria-induced hemolysis and proinflammatory cytokine production by dendritic cells are proposed mechanisms that may negatively affect the ability of phagocytic cells to respond to bacteremia, thus facilitating the spread of bacteria. [4].

Due to limited awareness in non-endemic regions, imported malaria in high-income settings may have high mortality and risk of delayed diagnosis. [5]. We present a single case of concomitant Plasmodium falciparum and Bacillus cereus bacteremia in a previously healthy young woman. She contracted the infection while traveling in Tanzania, but fell ill after returning to Ohio.

Presentation of the case

A 27-year-old woman presented to the emergency department (ED) in Ohio with fever, nausea, vomiting, and watery diarrhea for three days. Thirteen days before her presentation to the ED, she had returned from a 30-day trip to Tanzania. While she was in Tanzania, she was asymptomatic and remained in an urban setting. On the day of her return trip to the US, she developed watery diarrhea and nausea. Three days later, she complained of fevers that occurred several times a day, worsening diarrhea, and dehydration. She then sought medical attention. She denied having a headache, rash, respiratory symptoms, or sore throat. While she was in Tanzania, she reported mosquito bites. She supported eating home-cooked meals and drinking bottled water, but she drank tap water a few times while she was in Tanzania. She denied any sick contact. She was advised that she take a prescription medicine for the prevention of malaria, but she was unable to get it before traveling.

The patient had no medical history of interest and was not taking medication. He had received vaccinations against yellow fever, tetanus, influenza, COVID-19, hepatitis A, and meningococcus. He was born and raised in Tanzania and moved to the US as a teenager not mentioning any other recent international travel. This trip was his first trip to Africa since he moved to the United States.

In the ED, her temperature was 100.9°F, her pulse was regular and 120/minute, her blood pressure was 149/75, her respiratory rate was 17/minute and without difficulty, and her saturation was O2 was 99% while he was breathing ambient air. On physical exam, she appeared uncomfortable. She had no jaundice or neck lymphadenopathy. On auscultation, lung auscultation and heart sounds were normal. Her abdomen was tender at the epigastrium and there was no hepatosplenomegaly. The neurological examination of her was normal.

Laboratory examination revealed thrombocytopenia (129 k/uL), her hemoglobin was 12.5 g/dL with signs of hemolysis with a lactate dehydrogenase of 314 U/L. Her aspartate aminotransferase (AST) was 31 U/L and alanine aminotransferase (ALT) was 54 U/L. His sodium level was 132 mEq/L, potassium 3.1 mEq/L, blood urea nitrogen (BUN) 12, and creatinine 0.76 mg/dL (estimated glomerular filtration rate 110 mL/min). . Initial lactate was 2.4 mmol/L and improved to normal after fluid resuscitation.

Blood parasite analysis was performed with a Binax NOW Enzyme Immunoassay (EIA) for Plasmodium spp. Giemsa-stained thick and thin smears were obtained. The tests were confirmatory for P. falciparum with a parasitemia level of 1.9%. Enteric bacteria polymerase chain reaction (PCR) panel of stool specimen was negative for Salmonella, Shiga-like toxin-producing E. coli, Campylobacter, Shigella, enteropathogenic E. coli, enterotoxigenic E. coli, and E. coli. enteroinvasive coli. The ova and parasites test was negative for amoebas, helminths, or protozoa. PCR for Clostridium difficile was negative. On the second day of hospital stay, the blood cultures showed Gram-positive bacilli, which were confirmed the following day as the Bacillus cereus species (MALDI-TOF mass spectrometry). Additional tests for syphilis, HIV, dengue, chikungunya, and Zika virus were negative.

She was treated for uncomplicated malaria with artemether/lumefantrine for three days. The fever resolved on the third day in hospital, but diarrhea and dehydration persisted. Repeat blood smear on day three showed <0.1% parasitemia. Regarding B. cereus bacteremia, the decision was made to consider it a pathogen and not a contaminant because of persistent abdominal tenderness and watery diarrhea that required daily intravenous fluid resuscitation. After completing malaria treatment on day three, she was started on IV vancomycin 1 g every 12 hours the same day. On the second day of vancomycin, her diarrhea improved and on the third day her vancomycin diarrhea resolved. She was discharged on the fifth day of hospitalization, with instructions to take levofloxacin 750 mg daily for an additional seven days.


Bacillus cereus is a spore-forming, facultative anaerobic, Gram-positive bacillus. Ingestion of food contaminated with enterotoxigenic B. cereus or emetic toxin causes infection [6]. Diarrheal-like illness includes profuse watery diarrhea, abdominal pain and cramps, and sometimes nausea and vomiting. [7]. The onset of symptoms usually occurs within six to 15 hours of eating food that is left out at room temperature for more than two hours. Symptoms normally resolve within 24 hours of onset.

Limited information is available on the incubation period for Bacillus cereus bacteraemia in the literature. According to a review article on Bacillus cereus infections, the incubation period for B. cereus bacteremia can range from a few hours to several days, with a median incubation period of 18 to 24 hours. [6]. However, it is important to note that the incubation period may vary depending on the specific strain of B. cereus, the route of infection, and the individual’s immune status. One possibility is that the patient’s immune system was already compromised due to the presence of malaria, which may have made her more susceptible to developing bacteraemia. The observed incubation period for B. cereus bacteremia in the present case was significantly longer than the typical range reported in the literature. More research is needed to understand the factors that influence the incubation periods of this disease. [8].

B. cereus bacteremia is rare and is reported in the setting of intravenous drug use, central venous lines, or mucosal lesions, especially in immunosuppressed patients. The clinical presentation in B. cereus bacteremia can be dramatic, beginning with gastrointestinal symptoms and progressing to altered consciousness or even infective endocarditis. A 2007 study evaluating the susceptibility of Bacillus species to various antibiotics reported universal resistance to trimethoprim/sulfamethoxazole and beta-lactams. [9]. In that study, isolates were susceptible to quinolones, linezolid, streptomycin, tetracycline, tigecycline, and vancomycin by automated Sensititre® microbroth dilution and Etest® agar gradient diffusion methods. [9].

About 2,000 cases of malaria are diagnosed in the US annually, commonly in travelers and immigrants returning from countries where malaria transmission occurs. [10]. Coinfection with P. falciparum and B. cereus has not yet been reported in the literature. Here, initially, the positive blood culture was considered a possible contaminant, however, the patient was on her third day of malaria treatment and the fever resolved on the second day but the watery diarrhea persisted. The study for acute diarrheal diseases was negative and the patient was more dehydrated, requiring intravenous fluids. After starting vancomycin, the diarrhea rapidly improved and the patient was discharged to her home.

It is not clear why bacteremia is more common in patients with malaria. Theories have been suggested to investigate the impact of malaria on the immune system. The infection alters the production of proinflammatory cytokines by dendritic cells and suppresses the oxidative bursting capacity of neutrophils, allowing sustained bacterial replication. [11]. Unlike most bacteria, this phenomenon is well described only for Salmonella coinfection. Therefore, we report a single case of concomitant P. falciparum and Bacillus cereus bacteremia in a traveler returning to the US from Tanzania. Further studies are required to understand the mechanisms of this coinfection.


This case report highlights the importance of considering co-infection with Bacillus cereus bacteremia in patients with malaria, particularly those presenting with persistent watery diarrhea and dehydration. A complete medical history and laboratory study, including blood cultures and parasitemia levels, can aid in the accurate diagnosis of such cases. It is crucial to routinely obtain these tests from febrile patients returning from malaria-endemic areas, as bacterial co-infections may contribute to unresolved symptoms. This report contributes to a greater understanding of the relationship between malaria and Bacillus cereus bacteraemia, and underscores the need for greater awareness and vigilance in the diagnosis and treatment of these infections.

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