Antibiotic resistance, a major health issue
In France, antibiotic resistance causes an estimated 12,500 deaths per year, according to a 2015 report submitted to the Ministry of Health. The majority of deaths affect young children under 12 months and people over 65 years of age. Worldwide: 700,000 people die each year from drug-resistant diseases, including 230,000 from multidrug-resistant tuberculosis.
According to a report by a group of international experts, antibiotic resistance is expected to cause “10 million deaths per year” worldwide by 2050, more than cancer. The deaths would occur mainly in Asia (4.7 million) and Africa (4.1 million). In Europe, the study forecasts an annual average of 390,000 deaths. It would be 317,000 in the United States.
Evaluation of an antibiotic treatment
David Sontag and his team of researchers have developed a RL algorithm to validate a urinary tract infection treatment by prescribing antibiotics. The algorithm developed should guide the physician’s choice: prescribe the right antibiotic and avoid the phenomenon of resistance.
The dataset used
The dataset used to develop the algorithm is the AMR-UTI Dataset. It is a cohort consisting of 15,806 microbiological specimens collected from 13,682 women with UTIs between 2007 and 2016. The train set is composed of data from 2007 to 2013 and the test set is composed of data from 2014 to 2016.
The implemented RL model
The algorithm directly learns a policy π (Pi) from the input patient data X and an output treatment decision A (action space).
This decision is to give one of four antibiotics: nitrofurantoin (NIT), trimethoprim-sulfamethoxazole (SXT), ciprofloxacin (CIP) and levofloxacin (LVX).
NIT and SXT are first-line (narrow spectrum) antibiotics, while CIP and LVX are second-line (broad spectrum) antibiotics.
Narrow-spectrum (first-line) antibiotics kill only a limited number of bacteria. They can target and kill the bacteria that are causing the disease while leaving other bacteria alive, which may be beneficial. This type of antibiotic is usually prescribed when the doctor knows exactly which bacteria are causing the infection.
Broad-spectrum (second-line) antibiotics are effective against many different bacteria, including some that are resistant to narrower-spectrum antibiotics. This type of antibiotic is prescribed when the doctor is not sure which bacteria is causing the infection or when the illness is caused by several different bacteria.
The use of narrow-spectrum antibiotics limits the development of multi-drug resistant strains of bacteria.
The Reward Function
To train their reinforcement learning algorithm, the researchers chose :
- A patient agent (X),
- A policy to learn (π),
- An action (the antibiotic administered),
- A reward(r) computed based on the patient’s resistance to the antibiotic and the class of the administered antibiotic (narrow spectrum-first line/broad spectrum-second line).
- Treatment efficacy vectors Y are a function of a patient’s susceptibility to each antibiotic Yi (a) = 1 [patient i is susceptible to antibiotic a], treatment cost vector C is a function of the class of the selected antibiotic Ci (a) = 1 [a is a 2nd line antibiotic], and the composite treatment reward is a linear combination of the effectiveness and costs of each antibiotic using the preference ω ∈ [0, 1], given by ri =ω-Yi+(1-ω)-(1-Ci).
The cost function
The cost function chosen by David Sontag’s team to learn the π-policy is inspired by the “cost sensitive classification” previous works. It allows to transform a complex cost function into a simpler function to optimize.
The results obtained
The objective of the researchers is to define a policy (goal on the graph) that decreases both the use of broad-spectrum antibiotics (second-line) and the inefficiency of antibiotic treatment.
The trained model (blue circle) performs better than the physicians (red crosses) and the recommendations (diamonds).
For 1245 cases in which clinicians opt for second-line antibiotics, the algorithm selected first-line antiobiotics 1014 times without compromising favorable treatment outcomes.
For antibiotic recommendation for uncomplicated UTIs, the algorithm developed by David Sontag and his team reduced second-line antibiotic use by 50% and inappropriate treatment by 20%.
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