Increased resistance of Streptococcus pneumoniae isolates to antimicrobial drugs,at a referral hospital in north-west Ethiopia

Introduction

S. pneumoniae (pneumococcus) is a leading cause of bacterial pneumonia, meningitis, otitis media and sinusitis. This results in significant morbidity and mortality in patients suffering from pneumonia and meningitis. The pneumococcus is a common colonizing bacterium in the respiratory tract of children, where it is exposed to antimicrobial agents which can lead to resistance to the antimicrobial drugs. ¹

In the past, beta lactam antibiotics were very effective against S. pneumoniae. However, resistance to this class of antibiotics has become an increasing problem. ^2–4 Reports of penicillin resistant and multidrug resistant strains are being made in many different parts of the world. ^3–5 A number of penicillin resistant strains is also resistant to other drugs such as chloramphenicol, erythromycin, tetracycline and cotrimoxazole. ⁶

A retrospective analysis of paediatric meningitis cases at a referral hospital in Addis Ababa found that eight out of 46 children with pneumococcal meningitis (17%) were infected by penicillin resistant strains. ⁷

The aim of this study was to analyse the drug sensitivity pattern of S. pneumoniae isolates at Gondar University Hospital, Ethiopia. The institute is a tertiary level care and teaching hospital with 350 beds, catering for a population of 195,000 urban and three million rural inhabitants.

Methods

The records of the bacteriology unit of Gondar University Hospital were analysed retrospectively. All instances of S. pneumoniae isolates recorded between March 2001 and April 2005 were included. Data on the antibiotic susceptibility pattern of the isolates for each commonly used antibiotic were collected. The data were entered into computer and analysed using the EPI-Info version 6 statistical package program (Centers for Disese Control and Prevention). Chi-squared and Fisher's exact tests were used to compare proportions. P value 0.05 was taken as the cut-off point for determining statistical significance.

Blood agar and chocolate agar were used to isolate S. pneumoniae. All culture plates were incubated at 37°C, immediately after inoculation. The chocolate agar plates were incubated in a candle jar. The media were followed for up to 48 h. Colonies that were alpha haemolytic were isolated and tested for optochin sensitivity. The alpha haemolytic isolates with the characteristic colony feature of S. pneumoniae and were sensitive to optochin were presumptively taken as being S. pneumoniae. ⁸ The antibiotic sensitivity of the isolates was determined using the standard disc diffusion techniques. ⁹

Results

Between March 2001 and April 2005, S. pneumoniae was isolated from the clinical specimens of 59 patients seen at the hospital. Forty-two percent (22/53) of the isolates were taken from children under 15 years of age and 45.5% (25/55) of the patients were female. The majority of the isolates, 60% (35/58), were taken from the cerebrospinal fluid (CSF) and most, 69% (20/28), were from children under 15 years. Pneumococcal isolates were mainly found in children with ear discharge (8.6% [5/58]), ascites (8.6% [5/58]) and pleural fluid (8.6% [5/58]).

The isolates were found to be sensitive to cotrimoxazole (27% [14/52]), gentamycin (49% [25/51]), penicillin (69% [34/49]), tetracycline (71% [35/49]), ampicillin (77% [40/52]), chloramphenicol (88% [43/49]), erythromycin (88.5% [46/52]) and ciprofloxacin (91% [21/23]). Thirty-six of the 59 (61%) pneumococcal isolates were resistant to at least one drug and 14 (24%) were resistant to three or more antimicrobials.

The sensitivity pattern of S. pneumoniae isolates to the different antibiotics over the four-year study period is presented in Table 1. S. pneumoniae isolates taken after April 2003 have shown a significant decrease in their sensitivity to penicillin, cotrimoxazole and ampicillin.

Discussion

Drug resistant S. pneumoniae has been an increasing problem worldwide. Various studies are being conducted in order to assess the situation and devise the appropriate coping measures. ¹⁰ Unfortunately, in Ethiopia there is paucity of research being conducted.

This study clearly shows a high proportion of penicillin and multidrug resistant strains in our area. The Center for Disease Control published a report in 2002 on invasive pneumococcal disease in the USA, which showed that 34% were caused by pneumococci which were resistant to at least one drug and 17% by strains that were resistant to three or more drugs. ¹⁰ The corresponding results in our study were 61% and 24%, respectively. Similarly, the prevalence of penicillin resistant strains in our study (29%) is higher than the report from Addis Ababa, which showed a rate of 17%. ⁷ Furthermore, the isolates appear to be acquiring increasing resistance to crystalline penicillin, cotrimoxazole and ampicillin. This could be due to indiscriminate antibiotic prescribing.

In Ethiopia, crystalline penicillin is still used as first line drug in the treatment of severe pneumococcal infections. In view of these finding, it is imperative that larger studies are undertaken so that we can ascertain the necessity of revising this practice. The fact that most of the isolates were taken from the CSF of children underlines the seriousness of the issue.

Chloramphenicol, erythromycin and ciprofloxacin have been shown to be the most effective drugs in the treatment of S. pneumoniae isolates in our area.

Conclusion

This study has shown that a significant proportion of pneumococcal isolates in our area is drug resistant.