Abstract
Eight rodents were submitted for necropsy after being found in soft drink beverages. To determine whether the postmortem changes in these mice were consistent with contamination at the time of bottling/canning or after the beverage was opened by the consumer, we conducted a study of the effects of prolonged rodent submersion in soft drinks. Thirty unmanipulated laboratory mice, euthanized for other reasons, were placed in bottled beverages (diet and regular cola, sweet and unsweetened tea, seltzer water, and water) for time intervals ranging from 3 days to 2 months. Starting at the 1-week time point, all rodents submerged in sealed carbonated beverages at room temperature showed severe, full-body gas distention. This change was not seen if the bottle was uncapped or if the beverage was refrigerated. Other significant changes included staining of the incisors starting at 1 week in the colored beverages (colas, teas), and erosion of the occlusal surface of the incisors starting at 2 weeks in the acidic beverages (colas, teas, seltzer). Visceral decomposition increased with time in all the beverages, but was most rapid in the regular cola. The mice submitted for necropsy showed no gas distention, no incisor erosion, and visceral decomposition similar to the experimental mice at the 1-week time point. As the interval between production and opening ranged from 3 weeks to 3 months, these results suggest that the rodents entered the beverage containers after they were opened by the consumer.
Food contamination is recognized by the World Health Organization as a global challenge. 9 The Centers for Disease Control estimate that 1 in every 6 Americans gets sick from contaminated food each year, and the total cost of foodborne illness in the United States was estimated at $75 billion in 2023. 7 Rodents are well-established sources of microbes, such as Salmonella spp. and Leptospira spp., and are often implicated in foodborne disease. 10
Between 2018 and 2023, 8 rodents were submitted for diagnostic postmortem examination after being found in canned or bottled soft drinks by consumers (“diagnostic rodents”). The term soft drink, in the broadest sense, includes all nonalcoholic beverages. 12 These rodents were found in bottles of cola-flavored carbonated soda (5 regular, 1 diet) and 2 canned beverages (a carbonated energy drink and a flavored iced tea). The main goal of the postmortem examination was to determine whether the rodents entered the container during production or after opening by the consumer. This determination is largely based on estimation of the postmortem interval, which would be significantly shorter if the rodent entered the container after opening. An understanding of the order and rate of changes that occur after death as the carcass decomposes is required for estimation of the postmortem interval. These postmortem changes are influenced by a variety of environmental and carcass factors, many of which have been carefully studied in humans and other animals in terrestrial and, to a lesser degree, aquatic environments.2,5 The postmortem changes associated with submersion in a beverage inside a sealed container, however, are not well understood. Unique features of this postmortem environment include not just the aqueous component, but also protection from insects and scavengers, and some or all of the following: high pH, carbonation/increased pressure, sugar or artificial sweeteners, and beverage preservatives. Reports of postmortem changes in soft drink-submerged rodents are, to the authors’ knowledge, limited to an abstract describing a single mouse. 11
To better understand the effects of the soft drink environment on postmortem changes in rodents, we incubated euthanized laboratory mice (“experimental mice”) in carbonated and noncarbonated beverages and analyzed the postmortem changes at different time points under different environmental conditions. The results suggest some key features that can help determine the timeframe of rodent contamination of soft drinks.
Materials and Methods
To determine the effects of prolonged submersion of rodent carcasses in soft drinks, 30 unmanipulated adult (1- to 2-year-old) female laboratory mice (Mus musculus, C57BL/6 and Swiss Webster) that had been euthanized the same day for other reasons were placed in bottles containing different types of beverages and incubated for time periods between 3 days and 2 months. The beverages tested included carbonated sodas (regular and diet colas), tea (sweetened and unsweetened), seltzer water, and bottled water. The containers were opened and the weight of the mouse (using a calibrated Ozeri digital scale) and the pH of the beverage (using a calibrated Ruolan digital pH meter) were measured and recorded. The mice were manually inserted into the bottles and the bottles were recapped, except in 1 case, where the bottle was left open. The bottles were then incubated, either at room temperature (20-22°C, based on the thermostat settings in the room) or in a temperature-controlled cold room (4°C) until the extraction date. On the extraction date, the mouse was removed from the bottle (sometimes requiring the bottle to be cut open), examined, and scored for postmortem changes as described in Table 1. Each mouse was only evaluated at a single time point. After fixation in formalin, the maxillary incisors were examined and photographed using a dissecting microscope, and scored for erosion and discoloration (Table 1).
Scoring rubric.
The species of the 8 diagnostic rodents was determined based on appearance, morphometrics, and dentition. The degree of visceral decomposition and incisor erosion and discoloration were scored, as described in Table 1. In 2 cases, at the request of the individual requesting the necropsy, a sample from the mouse or the beverage was submitted for aerobic bacterial culture.
This study was exempt from requiring an animal use protocol by the Institutional Animal Care and Use Committee at Virginia Tech because the mice had been euthanized as part of other institutional animal care and use committee-approved studies.
Results
Characterization of Rodent Decomposition in Beverages
The treatment conditions and results of the experimental mice are listed in Supplemental Table S1. The experiments for sweetened and unsweetened tea were terminated at 2 weeks due to severe swelling of the bottles and concern for explosion. The bottles of uncarbonated water also swelled, but to a lesser extent, and these experiments continued for 2 months. The pH values for the uncontaminated beverages ranged from 3.5 (regular cola) to 7 (bottled water). The weight range for the experimental mice was 26 to 50 g. Mice heavier than 50 g would not fit into the bottles. Starting at the 1-week time point, all of the beverages had a foul odor which was easily detectable upon opening.
Postmortem changes in mice are pictured in Fig. 1 and scores for mice in cola, diet cola, water, and seltzer water are shown graphically in Fig. 2. As expected, visceral decomposition scores increased with length of submersion in all the beverages. Visceral decomposition was most rapid in the regular cola mice, and most of these mice had ruptured by the 2-week time period. At 2 months, visceral decomposition was severe for mice in all of the beverages (cola, diet cola, seltzer water, and bottled water). Refrigeration of the diet and regular colas delayed the rate of visceral decomposition at the 1-week time point and at 1 month for regular cola. By 2 months, visceral decomposition was similar to that seen in the room temperature beverages, although the mice in the refrigerated regular cola did not rupture.
Postmortem changes in mice submerged in soft drinks. (a) Regular cola, 3 days. Minimal changes. (b) Regular cola, 1 week. Note whole body gas distention and tearing of skin over the stomach. (c) Regular cola, 2 weeks. Severe gas distention and rupture of the body wall. (d) Regular cola, 2 months. The body wall has ruptured and the viscera are severely degraded. (e) Seltzer water, 1 week. Gas distention is similar to that seen with other carbonated beverages. (f) Diet cola, 1 week. Changes are similar to regular cola at 1 week (b), with more hair loss. (g) Water, 1 week. Gas distention is not a prominent feature. (h) Uncapped regular cola, 1 week. Gas distention is mild.
Graphical illustration of postmortem changes in mice submerged in soft drinks. Gray dash and dotted line, regular cola; dashed black line, diet cola; black dash and dotted line, refrigerated cola; solid black line, refrigerated diet cola; solid gray line, seltzer; gray dotted line, water. (a) Gas distention. Gas distention was most apparent in the regular cola, often leading to body wall rupture (score of 4). Diet cola and seltzer water also caused significant gas distention, with less severe distention in refrigerated beverages and minimal distention in water. (b) Visceral decomposition. Visceral decomposition was most rapid in regular cola, but was similar in all beverages by the 2-month time point. (c) Incisor discoloration. Incisors of rodents in colored beverages (soda and diet soda) showed variable degrees of discoloration, while no discoloration was detected in the clear beverages. (d) Incisor erosion. The scoring rubric is defined in Table 1, but in general, 0, no change; 1, mild change; 2, moderate change; and 3, severe change. A score of 4 is included for gas distention to indicate that the body was ruptured.
Severe gas distention of the tissues was observed in all of the mice submerged in closed carbonated beverages at room temperature. This change was evident starting at the 1-week time point and was similar in regular soda, diet soda, and seltzer water. These mice were characterized by extension of the limbs, bulging eyes, protruding tongues, and expansion of the viscera and subcutaneous tissues by gas bubbles. In some cases, the skin was split or the body wall was ruptured, usually starting in the left cranial ventral abdomen (over the stomach). The gas distended mice could not be extracted from the bottles without cutting the bottles open. This severe distention was not evident in the uncapped cola at 1 week, or in the refrigerated beverages, even after 2 months. Furthermore, the severe gas distention was not always associated with severe visceral putrefaction. The mice in noncarbonated beverages (water, sweetened and unsweetened iced tea) showed mild to moderate gas distention of the gastrointestinal tract and abdomen, but not the rigidity, bulging eyes, and subcutaneous gas distention evident with the mice submerged in carbonated beverages.
Changes in the incisor teeth of the submerged mice included discoloration and erosion (Fig. 3). Brown discoloration of the incisors was apparent in mice submerged in all of the colored beverages (diet and regular colas, sweetened and unsweetened tea). Incisor erosion was most severe in mice in regular cola (the beverage with the lowest pH) and the changes were similar in refrigerated and unrefrigerated mice in diet cola, starting at the 2-week time point. Incisor erosion was also apparent in the mice in sweetened and unsweetened tea and diet cola starting at the 2-week time point. Incisor erosion was not apparent in mice in water, but the mouse in seltzer water had significant erosion of the incisors at the 2-month time point.
Dental changes in mice submerged in soft drinks. (a-c) Teeth from mice submerged in regular cola at 1 week (a), 1 month (b), and 2 months (c). Note the discoloration, which is most obvious at 1 month, and the roughened occlusal surface at 2 months. (d-f) Diet cola at 1 week (d), 1 month (e), and 2 months (f). Changes are similar to those with regular cola with variable discoloration at all time points and roughening of the occlusal surface at 2 months. (g-i) Water at 1 week (g), 1 month (h), and 2 months (i). The black arrow points to the lateral notch which is a characteristic of Mus musculus incisors. Changes are minimal. (j-l) Seltzer at 1 week (j), 1 month (k), and 2 months (l). There are minimal changes at 1 week or 1 month. Erosion of the occlusal surface is apparent at 2 months.
Assessment of Diagnostic Rodents in Beverages
Of the 8 diagnostic rodents, 6 were submitted with the beverage container (Supplemental Table S2). In 2 cases, the production date of the beverage was known, and the time intervals between production and discovery were 20 and 30 days. The “best by” date was provided for 6 of the beverages, and the beverages were all opened before that date. The interval from known or suspected production date to consumption date ranged from 3 weeks to 3 months. Some of the mice had been found a year or more prior to the necropsy date and were stored frozen until they were submitted for necropsy. All of the mice were found in the containers in April, October, or November.
All 8 diagnostic rodents were identified as Peromyscus sp. (deer mice) based on size and dentition. The body weight, body length, tail length, and hind foot length were consistent with Peromyscus sp. measurements, and other small rodent species were excluded based on the lack of a lateral notch (a characteristic of the house mouse, Mus musculus, Fig. 3) or a rostral groove (a characteristic of the eastern harvest mouse, Reithrodontomys humulis) in the upper incisors. Six of the mice were female and 2 were male. One of the females was pregnant. A sample of the cola-type beverage from 1 case and a sample of abdominal fluid from the mouse in another case were submitted for aerobic culture, at the request of the individual requesting the necropsy, and Lactobacillus murinus was the only organism detected.
A definitive cause of death was not determined in any of the diagnostic rodents, although asphyxia due to drowning or lack of environmental oxygen was considered likely. Postmortem changes included some hair loss in the submerged parts of the body (especially in the rodents that had been frozen and thawed in the beverage) and mild to moderate visceral decomposition. None of these rodents were bloated or ruptured. The incisors were stained in the rodents in colored beverages (cola and diet cola), but no erosion was detected. The case details and gross findings in the submitted mice are summarized in Supplemental Table S2 and Supplemental Figure S1.
Discussion
This study used experimental mice to establish an approximate time course of postmortem changes for rodents submerged in soft drinks. That timeline was used to evaluate cases of potential rodent contamination of beverages. The changes in the experimental mice included gaseous distention, visceral decomposition, body wall rupture, and incisor discoloration and erosion.
The rigid gas distention of the mice in carbonated beverages was an unexpected finding. This change was not seen in the mice in refrigerated beverages or in the uncapped beverage. The gas expansion of these carcasses may be secondary to proliferation of anaerobic bacteria in the oxygen-poor/carbon dioxide-rich environment of a carbonated beverage, combined with the inability of carbon dioxide to diffuse out of the body or purge because of the high gas pressure inside the beverage container. In addition, studies have shown that skin is permeable to carbon dioxide, 6 so the gas may be diffusing from the beverage into the tissues along its concentration gradient. The visceral decomposition scores and likelihood of body wall rupture were highest in regular cola than diet cola, most likely because sugar promotes bacterial growth and replication better than artificial sweeteners.
Dental changes associated with exposure of teeth to soft drinks have been reported in humans and rodents. Brox et al 4 examined molars in mice consuming a regular cola beverage (instead of water) and found enamel erosion on the occlusal surface of the teeth at 2 weeks and erosion of both enamel and dentin at 4 and 6 weeks. The sugar content of the beverages may also contribute to enamel erosion, as oral bacteria can metabolize sugar to produce lactic and acetic acid, which further decrease the beverage pH. Discoloration of the teeth depends on both the content of the beverage and the health of the enamel. In a human study, Yay Kuscu and Gorus 15 showed that cola consumption caused tooth discoloration by comparing spectrophotometer readings of tooth color over the course of 1 month in dental students with no cola consumption, low consumption, or high consumption. The authors explain that staining of teeth is the result of chromogenic polyphenols in beverages that bind to protein within the tooth. Acidic beverages are more likely to cause staining because they etch the surface of the enamel, creating better retention of the chromogens and more surface area of protein exposure. Interestingly, in 2 of the beverages in this study (diet cola and refrigerated cola), staining of the incisors appeared less severe at later time points. A possible explanation for this finding is that prolonged exposure to the acidic environment either denatures the polyphenols or the protein that binds the polyphenols or otherwise inhibits the interaction between the protein and chromogen. Decomposition of submerged carcasses has not been as well studied as decomposition on dry land. According to Casper dictum, bodies decay on land approximately twice as fast as bodies in water. 1 The slower rate of decomposition is due to lower temperatures and decreased oxygen availability. A study of decomposition of submerged pig carcasses showed that the stages of decomposition tended to blend together, with carcasses exhibiting signs of bloat, active decay, and advanced decay at the same time. 1 An investigation of decomposition rates of mice in water 2 determined that water submersion delayed changes associated with decomposition, but these differences were attributed to delayed insect colonization.
The postmortem changes in all of the diagnostic rodents were most similar to those in the 7-day, uncapped beverage experimental mouse, suggesting a postmortem interval of 1 week or less (prior to freezing). In the mice that were frozen prior to necropsy, freezing should suspend the decompositional changes, but may introduce artifacts due to erythrocyte rupture and ice crystal formation. The post-production process of soft drink distribution typically takes at least a week, and usually the beverages do not reach consumers until several weeks up to a month or more after bottling/canning. For these 8 beverages, the known or suspected time intervals from production to consumption was between 3 weeks to 3 months. Of the 8 submitted mice, 7 were found in containers of carbonated beverages, but gas distention was not apparent at the time of necropsy. Although gas distention would likely subside after removal from the pressurized container and during the period of time prior to necropsy, which in some cases included freezing, bloating was not described by any of the consumers who found the rodents. Incisor erosion was also absent in all of the diagnostic rodents.
Although rodent contamination of soft drinks during production is not impossible, it is highly unlikely in modern facilities. Soft drinks are produced in a 2-stage process by 2 separate industries: one that makes the flavoring or syrup and one that manufactures and bottles the beverage. For carbonated soft drinks, the syrup producer blends the raw materials and packages the syrup concentrate for delivery to the bottler. Artificial sweeteners are added by the syrup manufacturer, while sugar (sucrose or high fructose corn syrup) is added by the bottler. The bottler also adds water and carbonation and seals the product in the container before shipment to the distributor or directly to a merchant. 13
Rodent contamination of soft drink containers could occur prior to or after filling. The rodents could not enter the bottle with the water or syrup, because these are injected with a small caliber nozzle. In most large-scale production facilities, a single machine inverts, rinses, fills, and caps the bottles or cans, all within a matter of seconds. The window of opportunity for rodent entry into the bottle or can is limited. Pest control efforts in food processing and packaging facilities include exclusion of rodents from buildings, as well as traps and chemical rodenticides within buildings. 3 Beverage containers are handled carefully to prevent rodent entry. The bottles and cans are stored upside down and are puffed with air to remove any foreign material prior to filling. The cans and bottles are sealed almost immediately after they are filled. Once filled and sealed, beverage cans and bottles are subjected to a variety of quality control procedures to ensure that the product does not contain any foreign material. These measures include weighing the final product, observing the level of the beverage, and, in some cases, radiography to scan for foreign matter.12,13
The conclusion in all 8 cases of the diagnostic rodents that were found in soft drinks was that the rodent entered after the product was opened by the consumer. In some cases, the history included information about the beverage being left in a vehicle, and rodents are notorious for entering and nesting in vehicles, often chewing wires and causing significant damage. In other cases, the beverage was handled by a young child, who may have been less vigilant about keeping the container closed or otherwise protected from pests than an adult. Interestingly, the time of year when the mice were found (April, October, and November) corresponds to times when Peromyscus sp. are shifting between winter and summer nesting locations and may be more likely to come into contact with humans. 14
Consumption of beverages contaminated by rodents, whether at the time of bottling or after opening, is a potential health risk as rodents can carry zoonotic pathogens. Lactobacillus murinus, which was the only organism cultured from a sample of one submitted beverage and fluid from another mouse, is part of the normal gut flora in rodents and does not cause disease in humans. In fact, this organism is considered a potential probiotic for conditions such as food allergy. 8 However, testing for anaerobic bacteria, fungi, protozoal, and viral contaminants was not part of this study.
Although this study provides a general timeline of decompositional changes in soft drink-submerged rodents, it has several limitations. First, only 1 mouse was subjected to most of the experimental conditions (specific time point, beverage type, temperature, open or closed container). As these mice were all unmanipulated, presumptively healthy, similarly sized, similarly aged, euthanized control animals, most of the individual factors that have been shown to influence decomposition rate (body mass and surface area, thickness of hair coat, cause of death, and age) were relatively constant. Two mice were tested in room temperature regular cola for 1 month, and the results were nearly identical. However, a larger study including multiple animals at each time may provide additional information about individual variation in decomposition rate. Second, the species of rodent used in the experimental study, Mus musculus, was different from the species of the diagnostic rodents (Peromyscus sp.). The experimental mice were larger than the diagnostic rodents, and higher body mass is often associated with slower decomposition. A study comparing decomposition of rats and mice did not report a significant difference in decomposition rate between the 2 species 5 ; however, to the authors’ knowledge, decomposition rates of Mus musculus and Peromyscus sp. have not been previously compared. Although the cause of death for the experimental mice (CO2 euthanasia) and diagnostic rodents (presumptive drowning or oxygen poor environment), was different, the physiologic mechanism leading to death (decreased oxygen in the lungs and cerebral hypoxia) was similar and decomposition would be expected to progress at a similar rate. Finally, the conditions associated with a rodent entering a beverage container during the bottling process could not be precisely replicated in this study. For the experiment, the sealed beverages were opened to insert the mice. Opening a carbonated beverage allows the air in the headspace of the bottle (the empty space above the liquid) to equilibrate with the air in the environment, and some of the carbon dioxide content is lost. For a 500 ml soft drink, the headspace volume is approximately 18 ml (3.4% of the total volume of the container). As CO2 is highly soluble in liquid (5-6 g/l at room temperature), the majority of the carbon dioxide in a full beverage container would be in the liquid, rather than the headspace. Therefore, a single opening would reduce the CO2 content in the bottle by less than 4%, which should have only a minor effect on the experimental results. The experimental conditions also differ from those of a rodent entering a container during the bottling process or after opening by the consumer in that the experimental mice were already dead at the time of entry. A living rodent would consume oxygen from and increase the carbon dioxide concentration in the headspace (of a closed container), and potentially change the chemical composition of the beverage slightly due to urination and/or defecation. However, again, these changes would not be expected to significantly affect the outcome.
In conclusion, this study describes the postmortem changes associated with prolonged submersion of rodents in soft drinks. Several of these changes, particularly severe gas distention (carbonated beverages) and incisor erosion (acidic beverages), are helpful in estimating the postmortem interval and determining the likely point of contamination.
Supplemental Material
sj-pdf-1-vet-10.1177_03009858251405485 – Supplemental material for Rodent contamination of soft drinks: An evaluation of postmortem changes
Supplemental material, sj-pdf-1-vet-10.1177_03009858251405485 for Rodent contamination of soft drinks: An evaluation of postmortem changes by Teresa Southard and Emily Falls in Veterinary Pathology
Footnotes
Correction (January 2026):
Article updated to correct the caption for Figure 1.
Supplemental material for this article is available online.
Author Contributions
E.F. and T.S. designed and performed the experiments. T.S. wrote the manuscript with contributions from E.F.
Declaration of Conflicting Interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
References
Supplementary Material
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