Changing trends in the profile of rodenticide poisoning

Abstract

Background

Deliberate self-poisoning (DSP) is one of the leading causes of mortality and morbidity, with rodenticides being common compounds used by many victims. However, comprehensive data regarding the spectrum and outcome of rodenticide poisoning is scant.

Method

This retrospective study was conducted in the Emergency Department (ED) of a large tertiary care hospital in South India between January 2017 and December 2018. All patients with deliberate consumption of rodenticides were included in the analysis.

Results

During the study period, 1802 patients presented with DSP, among which 145 (8%) consumed rodenticide compounds. The mean (SD) age was 27.9 (10.7) years. Young adults (16–30 years) comprised 73% (106/145) of the study population. The majority (87%) were triaged as priority 2, while 10% were triaged as priority 1. Common rodenticide compounds consumed were yellow phosphorous (57%: 82/145), coumarins (12%: 17/145), zinc phosphide (19%: 27/145), and aluminum phosphide (1%: 1/145). A significant proportion of patients (18.6%) were under the influence of alcohol. Among the 73 males, 25 (34.2%) gave a history of co-consumption of alcohol. There was a history of previous DSP attempts in 6%. The majority (68%) of the patients were discharged alive from the hospital, and the in-hospital mortality rate was 9%. Age >30 years (adjusted OR: 2.2; 95% CI: 1.00–5.05; p value: 0.04) was an independent predictor of poor outcome.

Conclusion

Rodenticide compound consumption for DSP is prevalent in young adults and is associated with significant mortality, especially with yellow phosphorous poisoning. The current trend in our country of the increasing use of highly fatal phosphorous compounds over the innocuous coumarin derivatives is a cause of grave concern.

Introduction

The use of pesticides as agents of deliberate self-poisoning (DSP) is on the rise, with more than 500,000 cases reported worldwide annually. ¹The 2017 Annual report of the American Association of Poison Control Centres and National Poison Data System (NPDS) shows a vast number of humans consuming poison with suicidal intent.¹ Suicide rates varied from 8.1 to 58.3/100,000 population in different parts of India.² In India, it was the most common cause of death in both the age groups of 15–29 years and 15–39 years.³ National Crime Records Bureau (NCRB) statistics of 2018 showed Tamil Nadu contributing 10.3% of all DSP in the country and is second only to Maharashtra.⁴ Rats are the most destructive pests causing a negative effect on the economy by damaging our agricultural crops. For preventing these pests, rodenticides are commonly used in our agricultural sector and homes, where these rodents often wreak havoc. The suicidal consumption of rodenticides is a major problem in Asian countries due to their easy availability. The composition and toxicity level of different types of rodenticides varies, with the majority being hepatotoxic, resulting in Acute Liver Failure (ALF). In the absence of a definite antidote, mortality in patients with rodenticide consumption is high.^5,6 In North India, aluminum phosphide is commonly used as a pesticide, rodenticide, and fumigant in the agriculture industry. The rapid action, easy availability, and high toxicity for the target species at an economic deal has made this compound an ideal agent with misuse for suicidal and homicidal poisoning. Phosphorous-based rodenticide poisoning is associated with a high mortality rate, and its toxicity has been widely described from cases across the world, from North India, United Kingdom, Australia, and Iran.^7,8,9,10 A recent study conducted in South India showed that yellow phosphorus was the most common rodenticide used in suicide attempts in this region, with 30% mortality despite maximal supportive therapy.¹¹ The clinical symptoms in patients with phosphine poisoning is fatal and include circulatory collapse, pulmonary edema, congestive heart failure, cardiac arrhythmia, and acute renal failure. Rodenticides are classified into low, moderate, and highly toxic compounds based on their potency to kill the rats. The higher toxic compounds are equally fatal to the human population.¹² There is a wide variation of the availability of pesticides in our country, and it is important to know the spectrum of compounds available in our geographic locality. This enables us to define the spectrum of complications or lethality associated with these compounds and helps us improvise our emergency preparedness and care. Hence, we conducted this study in our hospital to determine the profile of rodenticide compounds used for DSP in our catchment area and the hospital outcome.

Material and methods

Study design: This was a retrospective cohort study of patients who presented to the Emergency Department (ED) after consuming rodenticide compounds as a method of DSP.

Setting: The study was conducted in the ED of a large tertiary care hospital in South India. Our ED is a 50-bed department and tends to about 300 patients per day, including toxicology and nontoxicology patients.

Participants: All patients with acute rodenticide compound ingestion over eighteen years of age in the period from January 2017 to December 2018, presenting to the ED were included in the study. Confirmation of the type of poison was done purely by history. Most patients bring along the compound consumed and hence could be physically verified by the ED physicians. All patients were given standard, supportive care. Patients with yellow phosphorus and zinc phosphide compounds, if presented within 12 h of poisoning, were administered N-acetyl cysteine (NAC) as an antidote.

Variables: The charts were reviewed, and the relevant details of history, clinical findings, laboratory investigations were documented in the study form. The management in ED, the outcome of the patients from the ED with regards to admission, discharged, leave against medical advice, and hospital outcomes, were documented.

Outcome Variable: Hospital admission and outcome (mortality) were the outcome measures studied. A significant number of patients left the hospital against medical advice. This included patients with poor prognosis due to fulminant hepatic failure for which the relatives decided to take the patient home or to the local government hospital. These patients with “poor prognosis” were considered as having a “bad outcome” in the analysis.

Bias: This is a retrospective cohort study, and therefore, we could not control exposure or outcome assessment and instead relied on others for accurate record keeping.

Study Size: Based on a study by Mbarouk et al with an estimated prevalence of 1.2% and a precision of 4%, the sample size was calculated to be 118 patients. Therefore, we recruited patients over a one-year study period to reach the sample size.⁵

Statistical analysis: Analysis had been done using Statistical Package for Social Sciences for Windows (SPSS Inc. Released 2015, version 23.0. Armonk, NY, USA). Continuous variables are presented as mean (standard deviation). Categorical and nominal variables are presented as percentages. Factors for poor outcomes (Died or left against medical advice due to poor prognosis) were determined by bivariate, followed by multivariate logistic regression analysis, and their 95% confidence intervals were calculated. For all tests, a 2-sided p value less than 0.05 was considered statistically significant.

Results

During the study period from January 2018 to December 2018, 1802 patients presented with DSP to our ED, of which 145 presented with rodenticide poisoning (Fig. 1).

Fig. 1.

STROBE diagram.

Demographic profile: There was an equal gender distribution of 50%. The mean (SD) age was 27.9(10.7) years. Majority 87% (126/145) were triaged as priority II based on our ED triage guidelines; among these patients, 83% (120/145) were referred from another hospital. The rest of the characteristics are described in Table 1.

Table 1.

Baseline characteristics (N = 145).

Characteristics	Number (%)
Mean (SD) age in years	27.9 (10.7)
Male	73 (50.3)
Female	72 (49.7)
Age group
16–30 years	106 (73)
31–45 years	28 (19)
46–60 years	7 (5)
More than 60 years	4 (3)
Triage priority level
Priority 1	15 (10)
Priority 2	126 (87)
Priority 3	4 (3)
Other characteristics
Referred form another hospital	120 (83)
Known psychiatric illness	1 (1)
Previous history of deliberate self-poisoning/harm	9 (6)
Under the influence of alcohol	27 (19)

Associated risk factors: Deliberate ingestion of rodenticide under the influence of alcohol was seen in 27(19%). In our study, the major triggering factor for the deliberate ingestion of rodenticide was a domestic fight (49%). The percentage of associated risk factors such as the previous history of deliberate self-harm and known psychiatric illness were found to be 6% (n = 9) and 1% (n = 1) respectively.

Types of rodenticide consumed and outcome: The major rodenticide compounds ingested were yellow phosphorus (57%; n = 82), zinc phosphide (19%; n = 27), coumarin derivatives (12%; n = 17), and aluminum phosphide(1%; n = 1). The vital signs at admission and treatment in ED are shown in Table 2. Among the 8 patients requiring invasive ventilation in the ED, 7 consumed Yellow phosphorous, while 1 patient consumed Zinc phosphide.

Table 2.

Vital signs at ED arrival and resuscitation done.

Characteristics	Phosphorous compoundsa (N = 110) Number (%)	Coumarin compounds (N = 17) Number (%)	All rodenticides (N = 145) Number (%)
Vital signs
Tachycardia (HR > 100 beats/min)	43(39.1)	11(64.7)	57 (39.3)
Bradycardia (HR < 60 beats/min)	3(2.7)	0	3 (2)
Tachypnea (RR > 22/min)	36(32.7)	1(5.8)	38 (26)
Systolic Blood Pressure (SBP ≤ 90 mmHg)	21(19.1)	1(5.8)	25 (17)
SpO2 < 94%	8(7.3)	0	9 (6)
Low sensorium	7(6.4)	0	11 (8)
ED resuscitation
Invasive ventilation	8(7.3)	0	8 (6)
Vasopressors in ED	6(5.4)	0	7 (5)

^aIncludes Yellow phosphorous (n = 82), Zinc phosphide (n = 27) and Aluminum phosphide (n = 1).

The ED and hospital outcome is shown in Table 3 with 4/5th of the patients requiring hospital admission. The in-hospital mortality rate was 9% (13/145). However, 34 patients (23%) left the hospital against medical advice due to poor prognosis main reason being a fulminant hepatic failure. Among patients with a past history of DSP, there was no in-hospital mortality, while 2 patients left against medical advice due to poor prognosis. The in-hospital mortality rate among females was 11.1% (8/72) as compared to 6.8% (5/73) among males, which was not statistically significant (p value = 0.37, OR: 1.7; 95%CI: 0.53–5.47). In our study, of the 27 patients who were under the influence of alcohol, only 1 died. Co-consumption of alcohol did not have any statistically significant correlation with in-patient mortality (3.6% versus 96.3%; p value = 0.31, OR: 0.34; 95% CI: 0.04–2.73). We performed a bivariate analysis followed by multivariate logistic regression analysis to determine the factors for a poor outcome (death in ED or left against medical advice due to poor prognosis) compared to a good outcome (Treated and discharged stable from the hospital). Age >30 years (adjusted OR: 2.2; 95% CI: 1.00–5.05; p value = 0.04) was an independent predictor of poor outcome among patients presenting with rodenticide poisoning (Table 4).

Table 3.

ED and hospital outcome.

Characteristics	Number (%)
ED outcome (N = 145)
Intensive Care Unit/Ward admission	115 (79)
Discharged stable	10 (7)
Died in ED	3 (2)
Left against Medical Advice	17 (12)
Hospital Outcome (N = 115)
Discharged stable	88 (77)
Died	10 (9)
Left against Medical Advice	17 (14)

Table 4.

Bivariate and multivariate logistic regression analysis for factors associated with poor outcome.

Variables	Bad outcome N=(47)	Good outcome N=(98)	Bivariate analysis		Multivariate analysis
			P Value	Unadjusted Odds ratio (95%CI)	P value	Adjusted Odds ratio (95%C.I)
Age >30 years	21(44.7%)	25(25.5%)	0.02	2.36 (1.13–4.90)	0.04	2.2(1.00–5.05)
Priority1	10(21.3%)	5(5.1%)	0.06	5.02(1.60–15.60)	0.24	2.35(0.56–9.8)
SpO2 <94%	7(14.9%)	2(2%)	0.03	8.4(1.6–42.1)	0.94	0.91(0.68–12.42)
SBP <90 mmHg	4(8.5%)	1(1%)	0.03	9.02(0.93–83.1)	0.88	1.22(0.85–17.6)
Oxygen requirement	37(78.7%)	97(99%)	0.00	0.38(0.00–0.30)	0.22	0.48(0.00–0.64)

Poor outcome: Death in ED or left against medical advice due to poor prognosis.

Good outcome: Treated and discharged stable from the hospital.

Discussion

Our study highlights the profile and outcome of rodenticide poisoning, presenting to a tertiary care center in South India. DSP is a common cause of death in developing countries. Most of the suicides occur in the younger age group, as seen in our study. We found an equal incidence among men and women; this could be due to family feuds or domestic, violence resulting in impulsive consumption of the poison. Men in other studies have commonly found to use hanging followed by insecticide poisoning as method of harm whereas females resort to poisonings or self-immolation.⁵,⁶ Rodenticide is freely available over the counter in most shops as it is widely used in our country. Rats have been a menace leading to a rise in rodenticide use and production of various types of the same.

The outcome of any poisoning is largely based on the type of poison, the feasibility of immediate medical care, the amount of poison consumed, including time lapse in arrival at medical facility.⁹ Due to the tertiary level status of our hospital, most of our patients (82%) were referred from some other hospital; this could add to the delay and severity at presentation. Most of our patients, 44% presented later in the evening, which could be because of the domestic disputes occurring at home after work; these patients indulge in this behaviour when the family is sleeping or busy with their routine activities; this is similar to other studies where there is a belief that this group of patients have intent to die¹³. Our cohort of patients presented with respiratory distress with hypoxia and circulatory failure; this is in keeping with literature that suggests rodenticide poisoning results mostly in phosphine induced cardiac involvement, which manifests as circulatory collapse and pulmonary edema.¹⁴

We found yellow phosphorus was the most common type of rodenticide being used in 57% of our patients, which is more than the South Indian study done in 2016, which showed a 30% incidence, and they are usually associated with high mortality. This is in contrast to the type of poison used in Northern India, where metal phosphides are most prevalent.^15,16,17 Siwach et al found an incidence of 68% using aluminum phosphide with high mortality.¹⁸ These reports help us to understand the variation between the type of compound used in the Northern and Southern parts of India. Another interesting observation is that only 11% had consumed coumarin derivatives, and they had good outcome as they belong to the class of low toxic rodenticides. The rise is seen in the use of compounds other than coumarin derivatives, as they are relatively innocuous, whereas metal phosphides remain highly lethal, which is favorable for patients who consume with a suicidal intent. We also note that in countries like Taiwan and China, there is a consumption of predominantly coumarin-based compounds probably due to availability of the same and nonavailability of phosphorous based products in their country.^19,20,21 Comparison of outcome of patients presenting with various rodenticide compounds with other studies is shown in Table 5. It clearly showed significantly lesser mortality rates in places, where coumarin-based compounds are predominantly used as rodenticides, as compared to places in India, where the highly lethal phosphorous-based compounds are freely available and routinely used as rodenticides.

Table 5.

Comparison of the spectrum of rodenticide poisoning and outcome.

	Siwach et al.	Yu et al.	Yan et al.	Our study
Place	Rohtak, Haryana	Taiwan	China	Vellore, Tamil Nadu
Year of study	1995	2000–2011	2011–2012	2017–2018
Number of patients	403	20	177	145
Mean age (years)	27	35	32.2	27.9
Female sex		11 (55%)	55 (45%)	72 (50%)
Compound used
Coumarins		20 (100%)	177 (100%)	17 (12%)
Zinc phosphide	24(4.3%)			27 (19%)
Yellow phosphorous				82 (57%)
Aluminum phosphide	379 (68%)			1 (1%)
Unknown				18 (11%)
Mortality rate	256 (67.6%)	0	1/177 (0.56%)	13/145 (9%)

Treatment is predominantly supportive, and strong evidence for an effective antidote is currently unavailable, although there have been case reports on the use of NAC in yellow phosphorus poisoning with improved liver outcomes.¹⁷ In our study, 9% of our patients left against medical advice due to poor prognosis superadded with financial constraints as this subset of patients with fulminant hepatic failure required liver transplantation. A similar trend was reported in another study from South India as liver transplant is not a therapeutic option within reach of those with limited financial support.¹¹ In our study, we noticed a higher risk of mortality among patients aged more than 30 years, with many of them being the breadwinners of the family, further compounding the problem of arranging finances for an expensive option of a transplant. Recent studies suggest that a high Von Willebrand factor (VWF) level is a predictor of poor outcome and that lowering of vWF by NAC, fresh frozen plasma infusions, and plasma exchange (PLEX) improves patient outcome.²² Future research may be focussed on this vacuum in therapeutic options for phosphorous based rodenticides that could decrease mortality rates.

The perennial fact “prevention is better than cure” stands firm ground in this context. We need to employ strategies for rodent prevention so that the availability of rodenticides could be reduced on a large scale, thereby reducing the incidence of poisoning. We strongly recommend relevant authorities to implement stringent rules to restrict access to these compounds, which would be beneficial in reducing the incidence in our population.

Our study has certain limitations. This is data from a single medical center study, which results in patient selection and referral pattern bias. Missing charts and incomplete data were other limitations of our retrospective study. However, our study shows the common type of rodenticide poisoning and outcome in our region.

Conclusion

In our study, yellow phosphorus was the most commonly consumed rodenticide compound and is associated with high mortality. There is a worrying trend in our country with the increasing use of highly fatal phosphorous compounds over the innocuous coumarin derivatives. We recommend use of nonchemical rodent control to avoid mortality and morbidity associated with chemical rodenticide use for DSP.

Ethical considerations

This study was approved by the Institutional Review Board prior to the commencement of the study. Patient confidentiality was maintained using unique identifiers and by password-protected data entry software with restricted users.

Disclosure of competing interest

The authors have none to declare.