To our knowledge, this is the first study in India, which has attempted to quantify concurrently, in the same hospital, consumption of antibiotics, estimation of antibiotic residues in hospital-associated waters and antibiotic sensitivity amongst E.coli found in these waters.
From this study, it appeared that some of the antibiotics prescribed to the patients in hospitals are reaching the nearby aquatic environment. There was a positive, (though not statistically significant) correlation between antibiotic prescription quantity and residue levels in hospital effluent. Specifically for fluoroquinolones, the correlation was high. The reason for it not being statistically significant could be the small sample size in this study. Watkinson et al  also showed that the presence of antibiotics in hospital effluent depended on the volume of antibiotic prescription. They also found a positive correlation, which was not statistically significant. There are factors other than prescription volume that can play an important role in the quantities of antibiotics detected in the hospital effluent like the metabolism of antibiotics, their stability in the environment, temperature, water flow rate, time of sample collection, matrix effect, etc [1, 5].
Antibiotics from the fluoroquinolone group have also been found in hospital wastewater in other parts of the world. Amongst fluoroquinolones, ciprofloxacin was the most commonly found antibiotic in hospital effluent [1, 8–11, 22–24]. High residue levels of fluoroquinolones in the aquatic environment can cause genotoxic effects and can modify bacterial strains like Salmonella typhimurium at a residue level as low as 5 μg/l for norfloxacin and 25 μg/l for ciprofloxacin . In our study, the concentration of norfloxacin (6.4-29.6 μg/l) and ciprofloxacin (2.20-236.6 μg/l) in the drains was high, and this is a matter of concern in terms of its wider public health impact.
Ceftriaxone residue was not detected in any of the samples analyzed, despite the fact that it was one of the major antibiotics prescribed in the hospital. Neither have ceftriaxone and other antibiotics with the β -lactam ring generally been detected in hospital effluent elsewhere. Reasons for their non-detection have been cited as the easy degradation of the β -lactam ring, its high metabolic rate and the process of decarboxylation .
Results from the sampling repeated at the same point indicated that there were considerable variations in antibiotic concentrations detected at the same place over time. The residue levels of all the antibiotics from the fluoroquinolone group were higher at 16:00 hrs than at 10:00 hrs. Lindberg et al.  also reported considerable variation in residue levels when sampling was done at various times of the day at the same place. Such temporal variations might arise due to variations in the administration of antibiotics during the course of the day, water usage (and hence wastewater flow), as well as various pharmacokinetic factors such as metabolism, half-life and excretion rate [1, 5]. In addition, other processes such as sorption, hydrolysis and photolysis may influence the concentrations detected in wastewater at any particular time. In general, however, very little information is available on the temporal, spatial and diurnal behaviour of antibiotics in the aquatic environment. Longitudinal sampling strategies like monitoring of hospital effluents for antibiotic residues over several days with recording also of flow characteristics is needed to assess the potential risks associated with the release of these residues on environment in general and resistance in particular.
Several studies have documented the presence of antibiotic-resistant bacteria in the aquatic environment in general and hospital effluent in particular . It is not yet clearly established that the mere presence of antibiotic residues in the aquatic environment by itself influences the development of resistance in natural bacterial communities. It has been suggested that other factors like the density of resistant bacteria, duration of exposure to the antibiotic and presence of a favourable environment need to be considered as well . In our study, amikacin residue was not detected in any of the analyzed samples but nevertheless, E. coli from all the wastewater samples showed resistance to this antibiotic and even E.coli isolated from ground water displayed an intermediate behaviour. In contrast, none of the E.coli isolated from the wastewater samples was resistant to ciprofloxacin but showed intermediate behaviour in three samples, though high levels of ciprofloxacin residue were detected in the wastewater.
Antibiotics have been detected earlier in hospital effluent in high-income countries . The present study has highlighted the fact that antibiotics also enter the aquatic environment through hospital effluent in low- and middle-income countries. Unlike high-income countries, the situation can become more problematic in low- and middle-income countries, where resource constraints might result in untreated wastewater. In India, for example, not much wastewater undergoes any type of treatment and along with other pollutants; antibiotics must also be finding their way into recipient waters like rivers, lakes, reservoirs, etc. In situations where the wastewater is not subjected to any treatment, it is sometimes argued that antibiotics are diluted in the recipient waters in comparison with therapeutic concentrations and may not cause any harm. However, it is widely recognized that exposure to sub-therapeutic concentrations over long periods of time provides ideal conditions for the transfer of resistance genes. Use of non-culture techniques is important to understand the dynamics of transfer of antibiotic resistance genes. This was not possible in the present study, due to limited resources. However, we plan to use these techniques in future studies.
As regards the presence of resistant bacteria in the wastewater, treatment systems can be a way of combating this problem, as it has been shown that resistant bacteria are eliminated relatively efficiently in wastewater treatment plants . Further, from the point of view of low- and middle-income countries, low-cost, environment-friendly techniques could be designed and developed for the removal of antibiotics from wastewater using methods developed to simultaneously remove resistant bacteria. This may offer a comprehensive solution to the problem of antibiotic resistance development in the aquatic environment. We expect that the results of this study will be helpful in creating a basis for further scientific enquiry in India and other countries regarding the presence of emerging contaminants like antibiotics in environment and its impact on public health.