03. tbl. 108. árg. 2022

Invasive infections of Bacillus species in Iceland, 2006-2018

Ífarandi sýkingar af völdum Bacillus-tegunda á Íslandi árin 2006-2018

Anna Kristín Gunnarsdóttir1
Helga Erlendsdóttir2,3
Magnús Gottfreðsson3,4,5

1Department of psychiatry, 2Department of clinical microbiology, 3Department of infectious diseases, 4Faculty of Medicine, School of Health Sciences, University of Iceland, 5Department of science Landspitali University Hospital.

Correspondence: Anna Kristín Gunnarsdóttir, annakg@landspitali.is

Key words: Bacillus species, Bacillus cereus, penicillin resistance, invasive infections. sepsis, epidemiology, diagnostic criteria.

INTRODUCTION: The bacterial genus Bacillus is widely distributed environmentally and is usually considered a low-virulence organism, except for B. anthracis. A blood culture positive for Bacillus is often looked at as contamination. Nevertheless, B. cereus can cause invasive infections in humans and produces harmful toxins. The epidemiology of these infections remains poorly studied.

MATERIAL AND METHODS: All possible invasive infections caused by Bacillus during 2006-2018 at Landspitali University Hospital were identified from culture results. Clinical information was used to evaluate if there was a possible infection or confirmed infection. Here, the authors propose and use clinical criteria to categorize each case as contamination, possible infection or confirmed infection. The incidence of possible or confirmed infections was calculated using hospital catchment population data.

RESULTS: Positive cultures of Bacillus sp. from sterile sites during 2006-2018 were identified from 126 patients; blood (116), synovial fluid (8) and cerebrospinal fluid (2). In total, 26 cases were confirmed infection (20.6%), 10 possible infection (7.9%) and 90 contamination (71.4%). The incidence was 1.4 cases/100.000 inhabitants/year. Injection drug use was a risk factor among 11/26 patients with confirmed infection. The most common clinical presentation was sepsis. In this study, Bacillus was resistant to beta-lactam antibiotics in 92% of confirmed infections and 66% of the cases considered contamination (p=0.02).

CONCLUSION: Positive blood cultures of Bacillus sp. should be taken seriously, especially among patients with injection drug use, malignancy or immunocompromised state. It is important to draw two sets of blood cultures if there is a real suspicion of an infection to establish diagnosis and avoid unnecessary antibiotic therapy.

Table I: The table shows the criteria that was used to categorize the cases as confirmed infection, possible infection or contamination. To be categorized as confirmed infection patients had to meet at least 1 major criteria and 3 minor criteria or 5 minor criteria in total. To be categorized as possible infection patients had to meet at least 1 major and 2 minor or 3 minor critera in total.

Major criteria Minor criteria
> 2 positive blood cultures from same place but taken at different time. 1 positive blood culture if Bacillus is considered the most likely cause of infection.
>2 positive blood cultures from different places at the same time. 1 positive synovial fluid culture if Bacillus is considered the most likely cause of infection.
Positive cerebral spinal fluid culture and clinical symptoms of meningitis with no other possible cause of infection. Fever > 38°C
>2 positive synovial fluid cultures from the same place but at different time. Systemic symptoms
  Risk factors (intervention, foreign body, immune suppression, intravenous drug abuse, drug abuse within 48 hours).
  Laboratory results (WBC> 10 or < 4 x 109, CRP > 50 mg/L). Using the worst value< 24 hoursfrom taking positive blood culture and that there are not other likely explanations.

Table II: Number of positive cultures of Bacillus taken at Landspitali University Hospital from 2006-2018. Categorized by the site of positive culture.

Total (126) Confirmed infection (n=26) Possible infection (n=10) Contamination (n=90)
Blood 116 22 9 85
Synovial fluid 7 1 1 5
Blood and synovial fluid 1 1 0 0
Cerebral spinal fluid 2 2 0 0

Table III: The table shows the number of patients and their average age among with further categorization into the groups intravenous drug abuse (IDA), malignant disease and others. Furthermore, there is an information about the most common presentation and risk factor, how many patients had fever higher than 38°C and CRP higher than 50mg/L, if there was a suspected endocarditis, nosocomial infection or intervention. *Was not measured in two cases. 

Total (126) Confirmed Infection (26) Possible infection (10) Contamination (90)

Male 84 19 7 58
Female 42 7 3 32

Avarage age (standard deviation) 46,4 (25,7) 46,9 (18,9) 31,9 (19,1) 47,8 (27,6)

IDA 22/126 11/26 3/10 8/90
Malignant disease 30/126 6/26 4/10 20/90
Others 74/126 9/26 3/10 62/90
Other factors

Most common presentation
Bacteraemia / Septicaemia (14/26) Bacteraemia / Septicaemia(7/10)
Fever > 38°C
24/26 10/10
CRP > 50 mg/L
22/24* 8/10
Endocarditis suspected
6/26 0/10
Nosocomial infection
7/26 1/10
10/26 4/10

Picture 1: Distribution over the years 2006-2018. Number of positive blood-, cerebralspinalfluid- and synovial fluid cultures of Bacillusduring 2006-2018. Red is for confirmed infection, yellow is for possible infection and green is for contamination.

Table  IV: The table shows the number of strains in each category that was sensitive for penicillin.

  Total (n=126) Confirmed infection (n=26) Possible infection (n=10) Contamination (n=90)
Penisillínsusceptible (n=32) 2 2 28
Penisillínresistance (n=85) 22 7 56
Penicillin Intermediate susceptibility (n=1) 0 0 1
Susceptibility not checked (n=8) 2 1 5

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