MICROBIAL DRUG RESISTANCE Volume 3, Number 2, 1997 Mary Ann Liebert, Inc. Antimicrobial Susceptibilities and Capsular Types of Invasive Streptococcus pneumoniae Isolated in Children in Mexico City GABRIELA ECHÁNIZ-AVILES,1 MA. ELENA VELÁZQUEZ-MEZA,1 MARÍA NOEMÍ CARNALLA-BARAJAS,1 ARACELI SOTO-NOGUERÓN,1 FORTINO SOLÓRZANO-SANTOS,2 ADOLFO PÉREZ MIRA VETE,3 RODOLFO GATICA-MARQUINA,1 and JOSÉ LUIS Di FABIO4 ABSTRACT As part of the Sistema Regional de Vacunas (SIREVA) initiative, we conducted a surveillance study to de- termine the relative prevalence of capsular types of Streptococcus pneumoniae and antimicrobial susceptibil- ity of invasive isolates in children less than 5 years old. We collected 220 isolates and found 33 of the 90 known types, with type 23F as the most common followed by types 6A + B, 14, 19F, and 19A. High penicillin resis- tance was found in 49 strains (22.2-%), 31 belonging to type 23F. Twenty-nine (13.1%) were resistant to ery- thromycin, 95 (43.1%) were resistant to chloramphenicol, and 24 (10.9%) were resistant to cefotaxime. No strains were resistant to vancomycin. INTRODUCTION Infections caused by Streptococcus pneumoniae represent a serious public health problem in developing countries. Even though mortality rates caused by acute respiratory infections have decreased considerably during the last decade in Mexico, these diseases still represent the second most common cause of mortality among children younger than 5 years of age and accounted in 1992, for 8127 deaths in infants younger than 1 year of age (290.5 cases/100,000 persons). Among children from 1 to 4 years of age, there was a total number of deaths of 1470 (17.2 cases/100,000 persons).14 Considering pneumonia, studies performed in 13 developing countries demonstrated an overall bacterial etiology of 54.6% among children without antibiotic treatment and 22.9% among hospitalized children with antimicrobial treatment. The most frequent isolated bacteria were Streptococcus pneumoniae and Haemophilus influenzae, which were recovered in 45.5% and 28.4%, respectively, from percutaneous lung aspirates and 37.9% and 33.2% from blood cultures.2 Regarding S. pneumoniae meningoencephalitis, studies done by Muñoz et al.7 and Gamez et al.4 reported frequencies from two Mexican pédiatrie infectology units ranging from 13.6% to 14%. Certain characteristics such as a high population of chil- dren below 5 years of age, illiteracy, poor housing conditions, and serious pollution in big cities, favor the high morbidity and mortality rates caused by these infectious diseases. The use of penicillin as the drug of choice to treat infections caused by S. pneumoniae is hampered by an increased fre- quency of resistant strains to the drug in many parts of the world.1,16 Penicillin-resistant Streptococcus pneumoniae (PRSP) has been reported in Mexico since 1981 when Guis- cafré et al.5 reported 9 out of 117 strains with a minimal in- hibitory concentration (MIC) between 1.25 and 2 /xg/ml iso- lated from healthy children. In 1993, Calderón et al.2 reported 43.2% of PRSP among children attending a day care center and 12.8% among hospi- talized children in Mexico. The distribution S. pneumoniae types associated with infec- tions varies with age and region and may also change over time. There is a paucity of published data on type distribution of iso- lates that have been epidemiologically characterized in Latin America. With the help of the Pan American Health Organiza- tion, within the Regional Vaccine System (SIREVA), we con- ducted an epidemiological surveillance study to obtain crucial information regarding the distribution of invasive types and an- timicrobial susceptibility of S. pneumoniae among children un- der 5 years of age. This information will be useful to estimate coverage of proposed and potential pneumococcal conjugate vaccine formulas that are being developed in some parts of the world. 'Instituto Nacional de Salud Pública, Cuemavaca, Morelos, 2Hospital de Pediatría, Centro Médico Nacional, Siglo XXI, IMSS, 'Hospital In- fantil de México. México, 4Pan American Health Organization, Washington, DC. 153