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Journal of Clinical Orthopaedics and Trauma logoLink to Journal of Clinical Orthopaedics and Trauma
. 2024 Jul 28;55:102511. doi: 10.1016/j.jcot.2024.102511

Seasonal variation and preoperative risk factors for polymicrobial infection following open fracture

Madeline S Tiee a,⁎, Madeline M Lyons a, Philip G Ghobrial b,c, Cara J Joyce d, Ashley E Levack a, Garin G Hecht e
PMCID: PMC11345574  PMID: 39193376

Abstract

Introduction

Despite modern approaches to open fracture management, fracture-related infection (FRI) rates remain high. Recent studies demonstrated the seasonal and regional variation of causative organisms in FRI. This study aims to better understand the causative organisms and identify preoperative risk factors for the primary outcome of FRIs at a Level I trauma center.

Materials and methods

This retrospective cohort study examined all patients that underwent irrigation and debridement of an open fracture at a single Level I trauma center between 2007 and 2019. Exclusion criteria included gunshot wounds, hand injuries, and follow-up less than 3 months. Patients that developed FRI were compared by season, injury characteristics, patient demographics, initial management, and causative organisms.

Results

Among 695 patients with open fractures, 78 patients (11.2 %) developed infection, of which eight were Gustilo-Anderson (GA) Type I, 16 were GA Type II, 25 were GA Type IIIA, 26 were GA Type IIIB, and three were GA Type IIIC. Gram-positive FRIs were most common (81.1 %), followed by 56.8 % polymicrobial, 54.1 % gram-negative, and 10.1 % culture-negative infections. More than half (55.1 %) of the infections were from open tibial fractures and occurred after a motorcycle (32.1 %) or motor vehicle collision (23.1 %). Patients were more likely to have high FRI rates in the summer (12.8 %, n = 29) and fall (15.8 %, n = 32) in comparison of spring (4.7 %, n = 7) and winter (8.5 %, n = 10) (p < 0.01). Staphylococcus infections were more common in fall and winter (73.8 %, n = 31) versus spring and summer (44.4 %, n = 16) (p = 0.01). Patients that were transferred from outside hospitals had significantly higher rates of polymicrobial infection when compared to those who arrived from the field (63.6 % vs 41.2 %, p = 0.03). No differences were observed in infection causative organisms based on GA type.

Conclusions

Two preoperative risk factors for polymicrobial infection following open fracture include inter-hospital transfers and warm/humid weather. Broadening antibiotic prophylaxis during spring/summer months or for transferred patients may enhance antibiotic coverage and reduce infections.

Keywords: Open fracture, Gustilo-Anderson, Fracture-related infection, Seasonal, Polymicrobial, Osteomyelitis, Antibiotic prophylaxis

1. Introduction

Fracture-related infection (FRI) is a source of significant morbidity and mortality among patients with open fractures. Patients often require reoperation, longer hospital stays, and increased use of antimicrobials, which contribute to hospital readmission and healthcare costs.1, 2, 3 Infection rates for open fractures treated with surgical management are reported as about 6–7.6 % in the US and Canada,4,5 with a higher rate of 18.4 % (range 0.5–24 %) reported for low- and middle-income countries.6 A large scale analyses combining multiple studies reported overall rates for deep infection in open tibial shaft fractures to vary from 1.8 % for Gustilo-Anderson (GA) Type I open fractures to 16.1 % of Type IIIC.7 Another study looking at GA Type IIIB and severe IIIA open tibial shaft fractures found a 29.7 % risk of FRI.8 Risk of infection has been associated with the Gustilo-Anderson Type of open fracture, timely administration of appropriate antibiotics, and possibly time to surgical debridement.9, 10, 11, 12 It is widely accepted that timely administration of appropriate systemic antibiotics is an important factor that can decrease the incidence of infection after open fractures,10,11,13 and more recent data also suggests the importance of timely surgical debridement.14, 15, 16 Antibiotic regimens have remained similar to those first recommended by Gustilo and Patzakis in the 1970s and 1980s,9,12 and recent investigations have looked into the effects of local antibiotics in addition to systemic antibiotics in preventing FRI.17, 18, 19, 20 Of the risk factors for developing an FRI, antibiotic regimen remains one of the primary modifiable variables for preventing FRIs.

Previous studies have found seasonality and regional variability of both surgical site infections (SSIs) and FRIs for various types of orthopedic surgery. Studies on spinal surgery,21, 22, 23 hip fracture fixation,24 and primary total joint arthroplasty25, 26, 27 found higher rates of SSI and readmission/reoperation rates during the warmer and wetter months. For open extremity fractures in particular, Sagi et al.'s study of seven Level I trauma centers within seven different climatic regions in the United States showed significant seasonal and institutional variation.5,28 Infections were more common in the winter for the Northwest institution, summer and fall for the Northeast institution, spring and summer for the Southeast institution, and fall for Southwestern institution. Additionally, patients in the South and Northwest were more likely to have gram-positive FRIs. Patients with GA Type III injuries and also high injury severity scores (ISS) were more likely to develop infection. This seasonal variation is thought to stem from higher proliferation rates of skin flora in the setting of higher temperatures and humidity.29, 30, 31 In contrast, one study by Sanders et al.32 looked at infections after trauma-related foot, ankle, and lower extremity injuries and found no differences in seasonality of wound complications for their cohort. The authors attributed the lack of effect to be due to the temperate climate of the institution. These discrepancies in seasonality of infection could be due to regional variations in local climate. It is possible that the implementation of institutional protocols targeted at regional and seasonal variation in causative organisms of FRI may improve infection prevention for open fractures.

Given the institutional-level differences in antibiotic regimens, local antibiotic resistance profiles, and seasonal variations in temperature and humidity, more data is needed to understand the causative organisms in infection following open fracture and what modifiable preoperative risk factors exist to better prevent the outcome of FRI. This retrospective cohort study of open extremity fractures at a Level I trauma center in the Midwest region aims to determine what risk factors including seasonality may play a role in the risk of development of FRI.

2. Methods

This retrospective cohort study examined all patients that underwent irrigation and debridement of an open extremity fracture at a single Level I trauma center between 2007 and 2019 for the primary outcome of FRI. Approval for the project was provided by the Institutional Review Board. Patients that developed a FRI after initial injury were included up to three years after injury. Exclusion criteria included gunshot wounds, hand injuries, and inadequate documentation or follow-up for less than three months. Injury characteristics, patient demographics, injury severity score (ISS), transfer status from other hospitals, initial antibiotic and surgical management, and culture data (when available) were collected for all patients. Fractures were classified by the Gustilo-Anderson open fracture classification system by reviewing operative reports and medical records,9 and seasonality was defined according to previous articles:5,28 spring (March through May), summer (June to August), fall (September to November), and winter (December to February). Only deep infections that required a surgical debridement were included as part of our primary outcome. Infections were also classified based on if they met fracture-related infection (FRI) confirmatory criteria3 (Table 1). Patient radiographs and post-operative clinic documentation were also reviewed to determine time to union which was defined as having at least three bridging cortices on plain radiographs or having pain-free functional movement of the extremity.

Table 1.

Confirmatory criteria for a fracture-related infection.

Confirmatory Criteria for Fracture-Related Infection (FRI)
  • 1.

    Presence of fistula, sinus or wound breakdown (with communication to the bone or the implant).

  • 2.

    Purulent drainage from the wound or presence of pus during surgery.

  • 3.

    Presence of the same organism from at least two separate deep tissue/implant (including sonication-fluid) specimens taken during an operative intervention.

  • 4.

    Presence of one positive deep tissue or implant culture with other systemic suggestive signs of infection (fever, redness, joint effusion, elevated inflammatory markers).
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A total of 1207 patients underwent irrigation and debridement of an open fracture, of which 512 patients were excluded: hand injuries (n = 231), non-extremity injuries (n = 9), gunshot wounds (n = 132), pediatric patients (n = 37), no open fracture (n = 50), underwent surgery at an outside hospital (n = 9), expired or had poor follow-up (n = 33), or an amputation was performed acutely after injury (n = 61). Of the 695 total patients included in the study, 78 patients developed an infection after open fracture.

2.1. Statistical methods

Patient demographics and clinical characteristics were summarized overall and by season of injury. Associations of characteristics by season and polymicrobial infection were assessed for statistical significance using chi-square or Fisher's exact test as appropriate. A multivariable logistic regression model was developed using Firth's penalized likelihood approach due to small sample sizes. Analyses were performed using SAS 9.4 (SAS Institute, Cary, NC).

3. Results

Of the 695 patients with open fractures, 78 patients (11.2 %) developed FRIs. The overall incidence rate of FRIs were 11.7 % (62/531) for lower extremity open fractures and 9.8 % (16/164) for upper extremity open fractures. The incidence rate of infections for open tibial shaft fractures was 14.7 % (31/211). When looking at incidence rate of infection for all 695 patients with open fractures, there were 8.6 % (n = 60) gram-positive species, 2.7 % (n = 19) Methicillin-resistant Staphylococcus aureus (MRSA), 5.8 % (n = 40) gram-negative species, and 6.0 % (n = 42) were polymicrobial infections. No significant difference was noted in type of microbial infection between the upper and lower extremities (Table 2).

Table 2.

Treatment and infection characteristics.

Overall (n = 78) Spring (n = 7) Summer (n = 29) Fall (n = 32) Winter (n = 10) p-value
Infection incidence for all open fractures, % (n infection/n total) 11.2 % (78/695) 4.7 % (7/148) 12.8 % (29/226) 15.8 % (32/203) 8.5 % (10/118) 0.08
Length of stay, median (IQR) 14 (6–24) 23 (9–46) 13 (4–23) 14 (8–27) 12 (10–15) 0.37
Infection site, n (%)
 Upper extremity 16 (20.5) 3 (42.9) 7 (24.1) 5 (15.6) 1 (10.0) 0.32
 Humerus 7 (9.0) 1 (14.3) 4 (13.8) 2 (6.3) 0 (0.0)
 Forearm 7 (9.0) 1 (14.3) 3 (10.3) 3 (9.4) 0 (0.0)
 Humerus and forearm 2 (2.6) 1 (14.3) 0 (0.0) 0 (0.0) 1 (10.0)
 Lower extremity 62 (79.5) 4 (57.1) 22 (75.9) 27 (84.4) 9 (90.0) 0.35
 Pelvis 3 (3.8) 0 (0.0) 1 (3.4) 2 (6.3) 0 (0.0)
 Femur 10 (12.8) 1 (14.3) 2 (6.9) 4 (12.5) 3 (30.0)
 Tibia 43 (55.1) 3 (42.9) 16 (55.2) 18 (56.3) 6 (60.0)
 Foot 6 (7.7) 0 (0.0) 3 (10.3) 3 (9.4) 0 (0.0)
Antibiotics, n (%) [n = 76]
 Multiple 23 (30.3) 2 (28.6) 5 (17.9) 12 (38.7) 4 (40.0) 0.29
 Cefazolin 60 (78.9) 6 (85.7) 19 (67.9) 27 (87.1) 8 (80.0) 0.35
 Cefuroxime 4 (5.3) 0 (0.0) 4 (14.3) 0 (0.0) 0 (0.0) 0.09
 Gentamicin 28 (36.8) 2 (28.6) 5 (17.9) 15 (48.4) 6 (60.0) 0.03*
 Clindamycin 6 (7.9) 1 (14.3) 4 (14.3) 1 (3.2) 0 (0.0) 0.25
 Vancomycin 1 (1.3) 0 (0.0) 1 (3.4) 0 (0.0) 0 (0.0) 0.59
Hours to debridement, median (IQR) [n = 75] 6 (5–14) 8 (5–14) 8 (5–14) 6 (4–16) 6 (6–12) 0.68
Weeks to infection, median (IQR) 11 (4–23) 16 (3–43) 6 (3–18) 11 (5–23) 15 (4–25) 0.48
Use of local antibiotics in index I&D surgery, n (%) 24 (30.8) 1 (14.3) 10 (34.5) 8 (25.0) 5 (50.0) 0.37
Months to healing, median (IQR) [ n = 65] 6 (4–9) 7 (3–10) 6 (4–8) 6 (4–9) 8 (4–9) 0.84
Bone loss, n (%) 27 (34.6) 2 (28.6) 11 (37.9) 9 (28.1) 5 (50.0) 0.60
Organism was susceptible to original antibiotics given, n (%) [ n = 62] 37 (59.7) 3 (50.0) 11 (57.9) 16 (57.1) 7 (77.8) 0.72
Infection type, n (%) [n = 74]
 Most common organism MSSA (37.2 %) Enterobacter (57.1 %)/Enterococcus (42.9 %) MSSA (31.0 %) MSSA (37.5 %)/MRSA (31.3 %) MSSA (60.0 %)
 Polymicrobial 42 (56.8) 5 (71.4) 18 (62.0) 15 (46.9) 4 (40.0) 0.15
 Upper extremity, n (% of total UE) 12 (75.0) 2 (66.7) 6 (85.7) 3 (60.0) 1 (100.0) 0.31
 Lower extremity, n (% of total LE) 30 (50.0) 3 (75.0) 12 (66.7) 12 (44.4) 3 (33.3)
 MSSA 47 (63.5) 4 (57.1) 12 (41.4) 22 (68.8) 9 (90.0) 0.10
 Upper extremity, n (% of total UE) 12 (75.0) 2 (66.7) 5 (71.4) 4 (80.0) 1 (100.0) 0.25
 Lower extremity, n (% of total LE) 35 (58.3) 2 (50.0) 7 (38.9) 18 (66.7) 8 (88.9)
 MRSA 19 (24.7) 3 (42.9) 3 (10.7) 11 (34.4) 2 (20.0) 0.09
 Upper extremity, n (% of total UE) 5 (33.3) 2 (66.7) 1 (16.7) 2 (40.0) 0 (0.0) 0.47
 Lower extremity, n (% of total LE) 14 (23.3) 1 (25.0) 2 (11.1) 9 (33.3) 2 (22.2)
 Gram-positive 60 (81.1) 7 (100.0) 18 (62.0) 26 (81.3) 9 (90.0) 0.44
 Upper extremity, n (% of total UE) 14 (87.5) 3 (100.0) 5 (71.4) 5 (100.0) 1 (100.0) 0.67
 Lower extremity, n (% of total LE) 46 (76.7) 4 (100.0) 13 (72.2) 21 (77.8) 8 (88.9)
 Gram-negative 40 (54.1) 5 (71.4) 17 (58.0) 15 (46.9) 3 (30.0) 0.13
 Upper extremity, n (% of total UE) 7 (43.8) 2 (66.7) 3 (42.9) 2 (40.0) 0 (0.0) 0.26
 Lower extremity, n (% of total LE) 33 (55.0) 3 (75.0) 14 (77.8) 13 (48.1) 3 (33.3)
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n = number of patients, p = probability, IQR = interquartile range, I&D = irrigation and debridement, MSSA = methicillin-sensitive Staphylococcus aureus; MRSA = methicillin-resistant Staphylococcus aureus, UE = upper extremity, LE = lower extremity.

Of the 78 patients with FRI, the mean age was 45 years (SD 16.2) and 26.6 % were female (n = 21). The majority (79.4 %, n = 62) of patients developed an FRI after a lower extremity open fracture. Nearly half (39.7 %, n = 31) of patients with an FRI developed their infection after a tibial shaft fracture. The most common mechanisms of injury were motorcycle (32.1 %, n = 25) or motor vehicle collisions (23.1 %, n = 18). A large majority of patients with infections (74.4 %, n = 58) were polytrauma patients with other injuries besides their open fracture. The median ISS for our patients with infections was 17 (IQR 13–24) with more than half (57.7 %) being classified as either severe (ISS 16 to 25) or profound (ISS >25) ISS category (Table 3).

Table 3.

Patient characteristics by seasonality.

Overall (n = 78) Spring (n = 7) Summer (n = 29) Fall (n = 32) Winter (n = 10) p-value
Age, mean (SD) 45.0 (16.2) 57.9 (18.7) 45.0 (17.3) 41.6 (15.0) 46.7 (11.3) 0.11
Female, n (%) 21 (26.9) 3 (42.9) 9 (31.0) 9 (28.1) 0 (0.0) 0.14
Comorbidities, n (%)
 Diabetes 14 (17.9) 2 (28.6) 6 (20.7) 4 (12.5) 2 (20.0) 0.63
 Tobacco use 28 (35.9) 2 (28.6) 9 (31.0) 12 (37.5) 5 (50.0) 0.78
 Obesity 35 (44.9) 3 (42.9) 13 (44.8) 15 (46.9) 4 (40.0) 0.99
Transfer, n (%) 44 (56.4) 4 (57.1) 18 (62.1) 20 (62.5) 2 (20.0) 0.11
Polytrauma, n (%) 58 (74.4) 5 (71.4) 21 (72.4) 25 (78.1) 7 (70.0) 0.88
ISS, median (IQR) 17 (13–24) 13 (9–22) 17 (10–22) 18 (13–28) 18 (13–24) 0.19
ISS category, n (%)
 Minor 4 (5.1) 1 (14.3) 3 (10.3) 0 (0.0) 0 (0.0) 0.28
 Moderate 29 (37.2) 3 (42.9) 10 (34.5) 12 (37.5) 4 (40.0)
 Severe 28 (35.9) 2 (28.6) 13 (44.8) 9 (28.1) 4 (40.0)
 Profound 17 (21.8) 1 (14.3) 3 (10.3) 11 (34.4) 2 (20.0)
Mechanism of injury, n (%)
 MVC 18 (23.1) 3 (42.9) 7 (24.1) 5 (15.6) 3 (30.0) 0.64
 MCC/ATV 25 (32.1) 2 (28.6) 9 (31.0) 13 (40.6) 1 (10.0)
 Struck 11 (14.1) 0 (0.0) 3 (10.3) 5 (15.6) 3 (30.0)
 Fall 13 (16.7) 1 (14.3) 7 (24.1) 4 (12.5) 1 (10.0)
 Other 11 (14.1) 1 (14.3) 3 (10.3) 5 (15.6) 2 (20.0)
Gustilo-Anderson Type, n (%)
 I 8 (10.3) 0 (0.0) 5 (17.2) 3 (9.4) 0 (0.0) 0.10
 II 16 (20.5) 4 (57.1) 7 (24.1) 3 (9.4) 2 (20.0)
 IIIA 25 (32.1) 2 (28.6) 6 (20.7) 14 (43.8) 3 (30.0)
 IIIB 26 (33.3) 1 (14.3) 11 (37.9) 11 (34.4) 3 (30.0)
 IIIC 3 (3.8) 0 (0.0) 0 (0.0) 1 (3.1) 2 (20.0)
Gustilo-Anderson Type III, n (%) 54 (69.2) 3 (42.9) 17 (58.6) 26 (81.3) 8 (80.0) 0.09
Follow-up (months), median (IQR) 14 (6–24) 20 (10–24) 15 (8–24) 15 (12–30) 19 (12–34) 0.72
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SD = standard deviation, n = number of patients, p = probability, ISS = Injury Severity Score, MVC = motor vehicle collision, MCC = motorcycle collision, ATV = all-terrain vehicle, IQR = interquartile range.

When looking at patient characteristics by season, no differences were noted in patients with infections based on comorbidities, mechanism of injury, polytrauma status, or injury severity score between different seasons. Patients with infections with an injury that occurred in the spring were older (57.9 years) in comparison to patients injured in other seasons (45.0, 41.6, 46.7 years for summer, fall, and winter respectively) (p = 0.11). Additionally, patients transferred from an outside hospital made up larger proportions of patients with FRIs in the spring (57.1 %, n = 4), summer (62.1 %, n = 18), and fall (62.5 %, n = 20) in comparison to winter (20 %, n = 2) (p = 0.11). There was also a higher proportion of GA Type III injuries in patients with FRIs in the fall (81.3 %, n = 26) and winter (80 %, n = 8) in comparison to spring (42.9 %, n = 3), or summer (58.6 %, n = 17) (p = 0.09) (Table 3).

For these infections when examining causative organisms, 81.1 % (n = 60) involved gram-positive species, 54.1 % (n = 40) were gram-negative species, 56.8 % (n = 42) were polymicrobial infections, and 10.1 % (n = 8) were culture-negative (Table 2). About a quarter (24.4 %, n = 19) involved MRSA infection. Patients were most commonly given a 1st generation cephalosporin cefazolin (78.9 %, n = 60) and underwent an irrigation and debridement surgery at a median of 6 h after presentation (IQR 5–14). Patients with GA Type III open injuries were given a variety of antibiotic regimens including cefazolin alone (43.4 %, n = 23), cefuroxime (1.9 %, n = 1), gentamicin alone (11.3 %, n = 6), clindamycin (1.9 %, n = 1), cefazolin and gentamicin (37.7 %, n = 20), cefazolin and vancomycin (1.9 %, n = 1), and cefuroxime and gentamicin (1.9 %, n = 1). Fractures complicated by FRI were diagnosed at a median of 11 weeks (IQR 4–23) after injury and achieved union at a median of 6 months (IQR 4–9) (Table 2).

Infection rates differed by season: Patients had higher infection incidence rates in the summer (12.8 %, 29/226) and fall (15.8 %, 32/203) compared to the spring (4.7 %, 7/148) and winter (8.5 %, 10/118) (p < 0.01, Fig. 1). While not statistically significant, there may be some relationship between polymicrobial infections by season with more patients in spring and summer (63.9 %, n = 23) having polymicrobial infections in comparison to fall and winter (45.2 %, n = 19) (p = 0.16, Fig. 2). Polymicrobial infections were also significantly more prevalent among patients who had been transferred to our tertiary institution from an outside hospital (63.6 % vs 41.2 %, p = 0.03, Fig. 3). Gram-positive organisms were cultured at similar rates across the different seasons (p = 0.44) while in contrast, although not statistically significant, gram-negative organisms were more likely to be cultured during the spring and summer months (61.1 %, n = 22) in comparison to the fall and winter (42.9 %, n = 18) (p = 0.12). Methicillin-sensitive Staphylococcus aureus (MSSA) infections were more common in fall and winter (73.8 %, n = 31) in comparison to spring and summer (44.4 %, n = 16) (p = 0.01). MRSA was more commonly seen in spring (42.9 %, n = 3) and fall (34.4 %, n = 11) in comparison to summer (10.7 %, n = 3) and winter (20.0 %, n = 2) months (p = 0.09). In contrast, there were no differences in treatment by season in terms of antibiotics initially received, hours to debridement, and the use of local antibiotics in the index debridement surgery. There was also no significant difference in time to infection diagnosis and time to healing between fractures occurring in the different seasons.

Fig. 1.

Fig. 1

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Rates of fracture-related infection by season among all open fractures.

Pairwise comparison showed higher incidence of FRI in the summer and fall seasons when compared to spring and winter seasons (p < 0.01).

Fig. 2.

Fig. 2

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Rate of polymicrobial infection by season among those with any infection.

Pairwise comparison showed higher rates of polymicrobial infection in the spring and summer months when compared to the fall and winter months.

Fig. 3.

Fig. 3

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Rate of polymicrobial infection by transfer status among those with any infection.

A multivariable analysis showed that a large effect of transfer status on polymicrobial infection was maintained when controlling for seasonality and Gustilo-Anderson Type. Patients that were transferred from an outside hospital were at 2.51 times higher odds of developing a polymicrobial infection (95 % CI: 0.89–7.08; p = 0.08) (Table 4).

Table 4.

Adjusted odds ratios for characteristics associated with polymicrobial infection among those with infection type known.

Odds ratio (95 % Confidence Interval) p-value
Season
 Fall 1 (ref) 0.33
 Winter 1.16 (0.25–5.39)
 Spring 2.74 (0.44–17.0)
 Summer 2.75 (0.86–8.84)
Transfer
 No 1 (ref) 0.08
 Yes 2.51 (0.89–7.08)
Gustilo-Anderson
 Type I/II 1 (ref) 0.91
 Type III 1.07 (0.35–3.28)
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4. Discussion

For open fractures, seasonality and local climate may be important factors to consider in addition to other known risk factors for FRI including antibiotic administration, fracture severity, and surgical debridement.9, 10, 11, 12 Our retrospective study found that there are seasonal patterns to the infections associated with open fractures. Similar to our study, surgical site infections have been noted to increase in warmer and more humid seasons generally and for various orthopaedic surgeries including spinal surgery, total joint arthroplasty, and hip fracture surgery.21, 22, 23, 24, 25, 26,28,33,34 Seasonal variation in infections are thought to be a consequence of higher pathogen proliferation and survival outside the host during warmer and more humid months.29, 30, 31 Additionally, host behavior is more conducive to the spread of microbes during these same periods due to increased skin-to-skin contact, outdoor recreational activities, and changes to dietary consumption.29, 30, 31 These studies overall point to the importance of local environmental heterogeneity that may change the infectious landscape of open fractures in different seasons and locations.

For open fractures more specifically, previous studies by Sagi et al.5,28 similarly found seasonality in infections for particular areas of the United States including the Northwest, Southwest, Northeast, and Southeast regions. However unlike our study, they did not find seasonal differences in infection for their Midwest institution. We had an overall infection incidence of 11.2 % which is nearly twice the rate of Sagi et al.'s5 incidence rate of 5.5 % for the Midwest institution. Additionally, our study had the highest rates of infection during the summer (12.8 %) and fall (15.8 %) months, while their study found higher rates in the winter (6.4 %), summer (6.3 %), and fall (5.4 %) months. These differences could be contributed to differences in the severity of injury of patients however we cannot directly compare since their study gives overall ISS for all patients with open fractures and not just the patients with infection. Additionally, their study only looked at lower extremity injuries whereas our study included both lower and upper extremity injuries. Seasonality and local climate both seem to play a role in the infections seen in open fractures, and more research is needed to understand the specific factors that lead to these variations.

Furthermore, there were differences in what types of organisms were cultured for infections resulting from open fractures. Similar to previous studies, we found high rates of gram-positive organisms overall.5,22,28 MSSA was the most prevalent organism isolated for all our patients. We had the highest rates of MRSA infections during the spring, similar to Sagi et al.'s study where MRSA was the most commonly encountered organism for multiple institutions during the spring in the Midwest, Northeast, Southeast, and South institutions.5 Other studies looking at MRSA infections generally in pediatric and adult patients found highest rates of community-acquired MRSA in the summer and fall months.29,35 Another study noted higher rates of MRSA infection after lumbar spine fusion surgeries in the summer.34 For our study and Perencevich's study30 looking at general infections at a Maryland hospital, gram-negative infections were more prevalent during the spring and summer months. For a study looking at blood culture pathogens throughout the United States, there were not only higher rates of gram-negative bacteremia in the summer but also higher rates of imipenem-resistant Acinetobacter and Pseudomonas.36 In the current analysis, the spring and summer months were the seasons when both gram-negative and polymicrobial infections were more prevalent. One theory for the increase in gram-negative rod and aquatic organisms such as Pseudomonas during the summer months is more frequent aquatic recreational activities including swimming in pools or lakes where people can come in contact with these organisms.30 These differences may suggest locally important environmental differences that may be more favorable to different infectious organisms, particularly antibiotic-resistant pathogens, during various seasons.

One interesting finding of our study was that transferred patients more commonly had polymicrobial infections. Furthermore, while not statistically significant, transferred patients with infections made up more than half of the patients with infections during the spring, summer, and fall months in comparison to only 20 % of winter patients. These differences may be due in part to delayed care, increased exposure to multiple environments with high contact rates with various hospital staff and emergency response workers.37 Additionally, transfers often can result in delay to surgery and risks of miscommunication about antibiotic administration between institutions. Another possibility is that patients transferred to a tertiary center may be more likely to be polytraumatized with high injury mechanisms which can play some part in infection risk.38,39 One previous study suggested the finding of a “July effect” in which complication and infection rates increased in the summer months due to influx of new staff and trainees at teaching institutions,40 however subsequent studies showed no difference in outcome.41, 42, 43 Our study does suggest that transferred patients may be uniquely at risk for polymicrobial infections due to increased exposure and delay of definitive care. More research is needed to better understand how to decrease this risk and if using prophylactic antibiotics with broader coverage for transferred patients may have some utility.

The major limitation of this study was the retrospective nature of the study for a single hospital in one geographical area. Our study may also underestimate the number of infections after open fractures; we only captured patients who had their initial irrigation and debridement procedure for an open fracture at our facility and excluded patients who presented to other hospitals for their infectious complications. Additionally, the use of local antibiotics including vancomycin powder, antimicrobial irrigation and duration of intravenous antibiotics administration was variable depending on physician preference between patients which could alter FRI risk. Furthermore, our study was limited in the number of patients available for subgroup analyses.

This retrospective study provides additional evidence for the importance of local environment and climate on the development of infections in patients with open fractures. With the rise of antibiotic resistance and increased incidence of resistant pathogens such as MRSA, more research is needed across a wide diversity of environments throughout the country to truly understand the landscape of open fracture infections. Our study identified two preoperative risk factors for polymicrobial infection for open fractures at our Midwest institution: inter-hospital transfers and warmer humid weather in the summer and fall. The selective use of broader antibiotic prophylaxis for patients who meet these two risk factors of transferred status and injury during the warmer humid months has the potential to decrease FRI risk overall. Importantly, however, this strategy must be exercised cautiously and with antibiotic stewardship thoughtfully in mind to prevent exacerbating issues of antibiotic resistance.

CRediT authorship contribution statement

Madeline S. Tiee: Conceptualization, Methodology, Formal analysis, Investigation, Data curation, Writing – original draft, Writing – review & editing, Visualization. Madeline M. Lyons: Conceptualization, Methodology, Formal analysis, Investigation, Data curation, Writing – original draft. Philip G. Ghobrial: Investigation, Data curation, Writing – review & editing. Cara J. Joyce: Methodology, Formal analysis, Writing – review & editing. Ashley E. Levack: Conceptualization, Methodology, Supervision, Writing – review & editing. Garin G. Hecht: Conceptualization, Methodology, Supervision, Writing – review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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