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Microorganisms responsible of nosocomial infections in the Instituto Mexicano del Seguro Social

How to cite this article: Arias-Flores R, Rosado-Quiab U, Vargas-Valerio A, Grajales-Muñiz C. Microorganisms responsible of nosocomial infections in the Instituto Mexicano del Seguro Social. Rev Med Inst Mex Seguro Soc. 2016;54(1):20-4.



Received: August 5th 2014

Accepted: September 1st 2015

Microorganisms responsible of nosocomial infections in the Instituto Mexicano del Seguro Social

Rafael Arias-Flores,a Ulises Rosado-Quiab,b Alfredo Vargas-Valerio,a Concepción Grajales-Muñizc

aÁrea de Vigilancia Epidemiológica Hospitalaria, División de Enfermedades Transmisibles

bJefatura del Área de Vigilancia Epidemiológica Hospitalaria, División de Enfermedades Transmisibles

cJefatura de la División de Enfermedades Transmisibles

Coordinación de Vigilancia Epidemiológica, Instituto Mexicano del Seguro Social, Distrito Federal, México

Communication with: Rafael Arias-Flores

Thelephone: (55) 5336 0008, extensión 15759


Background: The prevention and control of the nosocomial infections involve the knowledge of the most frequent type of microorganism isolated. In Mexico there are not national statistics to identify the main microorganisms that cause a nosocomial infection.

Methods: It was conducted an analysis of all the culture results of the nosocomial infections reported by the Sistema de Vigilancia Epidemiológica Hospitalaria (Epidemiological Surveillance System) of the Instituto Mexicano del Seguro Social during the year 2013. The most frequent and relevant microorganisms were reported.

Results: 48 377 results from cultures of nosocomial infections were studied. Of these 13 207 (27.3 %) were from 25 high specialty medical units and 35 170 (72.6 %) from 197 second level medical units. The most frequently isolated microorganism was Escherichia coli with 8192 results (16.9 %), followed by the group of Coagulase-negative Staphylococci with 6771 cultures (14 %) and Pseudomonas aeruginosa with 5275 results (19.9 %). Slight differences between levels of care and specialized hospitals were observed.

Conclusion: This study identifies the Escherichia coli, the group of Coagulase-negative Staphylococci and the Pseudomonas aeruginosa as the main microorganisms to prevent.

Keywords: Bacterial infections; Mycoses; Cross infection; Social security; Mexico.

Nosocomial infections or hospital-acquired infections are a global health problem that increases the costs of care and facilitates the selective generation of multidrug-resistant microorganisms. As there are a huge number of pathogenic species, it has been proposed to study a specific group that generates more resistance and is found in greater proportion in hospitals. This group has been called the ESKAPE group, by the first letter of each species:1

  • The E comes from Enterococcus faecium, whose importance is vancomycin resistance.
  • The S comes from Staphylococcus aureus, which is a methicillin-resistant organism. Oxacillin and methicillin are semisynthetic penicillins which are stable to staphylococcal beta-lactamase, thanks to the strategic location of certain lateral chains in the molecule. The resistance to these antibiotic markers identifies cross-resistance with beta-lactams.
  • The K comes from Klebsiella, whose production of extended spectrum beta-lactamases and carbapenemases are of great concern because resistance can be transmitted through plasmids between different species.2
  • The A comes from Acinetobacter baumannii, whose antibiotic multidrug resistance creates a challenge for international treatment recommendations.
  • The P comes from Pseudomonas aeruginosa, whose resistance to carbapenems and quinolones causes great concern in ventilator-associated pneumonia with this etiology.
  • The E refers to Enterobacteriaceae. This group includes E. coli and Morganella morganii among others.

The prevalence of these microorganisms and their resistance has been studied in countries like the United States or communities like the European Union. In the United States Staphylococcus aureus is reported as the most frequently isolated microorganism with 12,635 isolations (15.6%), followed by Escherichia coli with 9351 (11.5%), coagulase-negative Staphylococcus with 9261 (11.4%), Klebsiella (pneumoniae/oxytoca) with 6470 (8.0%), Pseudomonas aeruginosa with 6111 (7.5%), Enterococcus faecalis with 5484 (6.8%), Candida albicans with 4275 (5.3%), Enterococcus faecium with 3314 (4.1%), and Acinetobacter baumannii with 1490 (1.8), among others.3

On the other hand, the European Union determined in its prevalence point study that Escherichia coli (177: 15.2%) is the microorganism most frequently associated with nosocomial infection, followed by Staphylococcus aureus with 141 (12.1%), Pseudomonas aeruginosa with 121 (11.2%), coagulase-negative Staphylococcus with 97 (8.3%), Klebsiella spp. with 94 (8.1%), Candida spp. with 56 (4.8%), Enterobacter spp. with 49 (4.2%), and Acinetobacter spp. with 49 (4.2%), among others.4

In Mexico the closest thing to these investigations mentioned is a national survey conducted by the Secretaría de Salud in 2011. This study identified that in 914 infections the main microorganism isolated was Enterobacter spp. (38%), followed by Staphylococcus aureus (13%), Pseudomonas spp. (13%), coagulase-negative Staphylococcus (8%), Acinetobacter spp. (7%), Enterococcus spp. (6%) and Candida spp. (5%), which showed a very different biota than that reported internationally, so the need arose to identify the main microorganisms causing nosocomial infections in the Instituto Mexicano del Seguro Social (IMSS).5


An analysis was made of all positive cultures of nosocomial infections detected by the Unidad de Vigilancia Epidemiológica Hospitalaria (UVEH) throughout 2013, information that was collected by the IMSS Coordinación de Vigilancia Epidemiológica (CVE). The Institute has allotted the presence of one UVEH in each hospital, consisting of at least one medical epidemiologist and a public health nursing specialist; depending on the size of the hospital, the required number of UVEH members increases. This unit detects nosocomial infections and prepares a final report to summarize it at the CVE administrative level. This report registers the number of isolated microorganisms whose final concentration is presented.   

IMSS has a total of 197 secondary care hospitals, divided into 127 general hospitals, 26 regional area hospitals, 35 general subzone hospitals, and nine OB-GYN/pediatrics hospitals, as well as 25 highly specialized medical units (UMAE) and an infectious disease hospital as tertiary care units. Among the UMAEs there is a single-specialty hospital for oncology, one for infectious disease, two high-specialty hospitals for children, two for cardiology, 10 high-specialty hospitals for adults, five high-specialty OB-GYN hospitals, five for trauma and orthopedics, and a general hospital with 523 registered beds and 232 unregistered beds. Almost all medical units have a bacteriology department that identifies microorganisms using an automated VITEK MS system.   


48,377 results of nosocomial cultures were studied; of these, 13,207 (27.3%) were at UMAEs and 35,170 (72.6%) at second-level medical units. The most frequently isolated microorganism was Escherichia coli with 8192 (16.9%), followed by the group of coagulase-negative Staphylococcus with 6771 (14%), and Pseudomonas aeruginosa with 5275 (19.9%), as shown in Table I.

Table I Main microorganisms isolated from nosocomial infections in medical units of the Instituto Mexicano del Seguro Social in 2013
IMSS medical units Second-level medical units UMAE
n % n % n %
Escherichia coli 8192 16.9 6282 17.9 1910 14.5
Staphylococcus aureus 4725 9.8 3534 10.0 1191 9.0
Coagulase- negative Staphylococcus 6771 14.0 4899 13.9 1872 14.2
Klebsiella pneumoniae 3122 6.5 2118 6.0 1004 7.6
Klebsiella oxytoca 371 0.8 268 0.8 103 0.8
Acinetobacter spp. 1437 3.0 690 2.0 747 5.7
Pseudomonas aeruginosa 5275 10.9 3721 10.6 1554 11.8
Enterobacter cloacae 1696 3.5 1158 3.3 538 4.1
Candida albicans 3115 6.4 2499 7.1 616 4.7
Other 13673 28.3 10001 28.4 3672 27.8
Total 48377 100 35170 100 13207 100
UMAE = unidad médica de alta especialidad (highly specialized medical unit)

Comparing second-level units and third-level units, very slight differences can be seen, such as the fact that Pseudomonas aeruginosa is more common in UMAEs than in second-level hospitals. Another difference observed is the fact that Acinetobacter spp. is more common in UMAEs than in second-level hospitals, and Candida albicans is more frequently isolated in second-level hospitals than in UMAEs.  

Large differences between isolates were observed in the single-specialty third-level hospitals. The most notable difference was observed in the high frequency of Pseudomonas aeruginosa in adult UMAEs unlike all other UMAEs. As for trauma and orthopedics UMAEs, a higher frequency of Staphylococcus aureus was observed, while in the Oncology UMAE it was Escherichia coli and in the OB-GYN and pediatrics UMAE, it was coagulase-negative Staphylococcus (Table II).

Table II Main microorganisms isolated from nosocomial infections in unidades médicas de alta especialidad (highly specialized medical units) (divided by type) of the Instituto Mexicano del Seguro Social in 2013
Trauma and orthopedics UMAE OB/GYN UMAE OB/GYN and Pediatrics UMAE Adult UMAE Oncology UMAE
n % n % n % n % n %
Escherichia coli 250 9.6 228 21.2 168 13.1 841 15.2 84 42.4
Staphylococcus aureus 431 16.5 61 5.7 77 6.0 398 7.2 29 14.6
Coagulase-negative Staphylococcus 205 7.9 393 36.5 224 17.5 598 10.8 31 15.7
Klebsiella pneumoniae 188 7.2 82 7.6 114 8.9 389 7.0 9 4.5
Klebsiella oxytoca 24 0.9 10 0.9 11 0.9 39 0.7 6 3.0
Acinetobacter spp. 242 9.3 7 0.6 97 7.6 272 4.9 7 3.5
Pseudomonas aeruginosa 224 8.6 46 4.3 127 9.9 846 15.3 22 11.1
Enterobacter cloacae 121 4.6 27 2.5 64 5.0 214 3.9 4 2.0
Candida albicans 139 5.3 25 2.3 68 5.3 215 3.9 6 3.0
Other 785 30.1 198 18.4 330 25.8 1725 31.2 60 30.3
Total 2609 100 1077 100 1280 100 5537 100 198 100
UMAE: unidades médicas de alta especialidad (highly specialized medical units)


This study provides an overview of the main microorganisms isolated in nosocomial infections in all IMSS hospitals. IMSS being an institute that provides health care to nearly half of the Mexican population, we can say that this study can approximate a national etiology of nosocomial infections.

The nearest study to this study is a multicenter study of hospital-acquired infections by Mexico’s Secretaría de Salud, which shows large differences as to etiologies, identifying Enterobacter spp. in almost half of nosocomial infections, whereas in this study it was not even close to 5%; however, strong similarities were observed to the analyses presented by the United States and the European Union, as they identified Staphylococcus aureus and Escherichia coli as the top two microorganisms.

There was a difference regarding a high frequency of Pseudomonas aeruginosa, which may be because Mexico has the highest consumption of antibiotics registered in Latin America, which favors the natural selection of more resistant bacteria in hospitals, such as Pseudomonas aeruginosa.3-7

As for Staphylococcus aureus, its low frequency is striking compared to coagulase-negative Staphylococcus, especially because the frequency of this microorganism and its resistance to methicillin is an indirect indicator of the impact of nosocomial infection prevention policies in units such as the hand hygiene program, safe action plans, and antibiotic control. This finding is relevant and deserves to be studied, because it has been shown that coagulase-negative Staphylococcus that are resistant to methicillin are more likely to colonize health personnel than Staphylococcus aureus.8-10

Differences by type of specialty in highly specialized hospitals should be noted. This is due to the different ways that staff carry out procedures and the type of nosocomial infections that they have, as seen in the IMSS Sistema de Vigilancia Epidemiológica. For example, in trauma and orthopedics hospitals, the main type of infection is the site of surgical implants, an infection that precisely is more often associated with Staphylococcus aureus, which explains the high frequency of this microorganism in these hospitals.11,12 

For the Oncology UMAE, the main infection is of the surgical site in colorectal surgery; it has been shown that the main microorganism to prevent the occurrence of nosocomial infection is Escherichia coli, a justification consistent with the high frequency observed in this study.13

As for OB-GYN and pediatrics hospitals, their main infections are pneumonia and bacteremia, whose most common microorganisms in other countries are coagulase-negative Staphylococcus and Escherichia coli, similar to what was observed, while highly specialized adult units found Escherichia coli and Pseudomonas aeruginosa as the most common bacteria, and their main infections reported were pneumonia and urinary tract infections, an association similar to that reported in international studies.3,9

It is worth noting the high prevalence of Escherichia coli in all units, which is even more prevalent in second-level units. Chances are that this is due to a flaw in the hand hygiene program, since there is an evident lack of removal of microorganisms that temporarily colonize the skin, which is more noticeable in second-level hospitals than in third-level.14-18

A weakness of this analysis is that it lacks specific information on certain species of microorganisms, so, for example, it lacks an adequate statistical frequency of Enterococcus; however, the frequencies of the most common microorganisms documented in international literature is available. The current surveillance system cannot provide the resistance of microorganisms, so the next step will be to develop a way to capture and analyze the frequency of antibiotic resistance of all microorganisms causing nosocomial infections.

  1. Boucher HW, Talbot GH, Bradley JS, Edwards JE, Gilbert D, Rice LB, et al. Bad bugs, no drugs: no ESKAPE! An update from the Infectious Diseases Society of America. Clin Infect Dis. 2009;48(1):1-12.
  2. Pan YS, Yuan L, Zong ZY, Liu JH, Wang LF, Hu GZ. A multidrug-resistance region containing blaCTX-M-65, fosA3 and rmtB on conjugative IncFII plasmids in Escherichia coli ST117 isolates from chicken. J Med Microbiol. 2014;15. doi: 10.1099/jmm.0.070664-0.
  3. Sievert DM, Ricks P, Edwards JR, Schneider A, Patel J, Srinivasan A, et al. Antimicrobial-resistant pathogens associated with healthcare-associated infections: summary of data reported to the National Healthcare Safety Network at the Centers for Disease Control and Prevention, 2009-2010. Infect Control Hosp Epidemiol. 2013;34(1):1-14. doi: 10.1086/668770. Epub 2012 Nov 27.
  4. Zarb P, Coignard B, Griskeviciene J, Muller A, Vankerckhoven V, Weist K, et al. The European Centre for Disease Prevention and Control (ECDC) pilot point prevalence survey of healthcare-associated infections and antimicrobial use. Euro Surveill. 2012 Nov 15;17(46). pii: 20316.
  5. Secretaría de Salud. Medición de la prevalencia de infecciones nosocomiales en hospitales generales de las principales instituciones Públicas de salud. México: SSA; 2011. [citado 19 Mar 2014]. Disponible en
  6. Wirtz VJ, Dreser A, Gonzales R. Trends in antibiotic utilization in eight Latin American countries, 1997-2007. Rev Panam Salud Publica. 2010;27(3):219-25.
  7. Rosenberg C, Boistard P, Dénarié J, Casse-Delbart F. Genes controlling early and late functions in symbiosis are located on a megaplasmid in Rhizobium meliloti. Mol Gen Genet. 1981;184(2):326-33.
  8. Borg MA. Lowbury Lecture 2013. Cultural determinants of infection control behaviour: understanding drivers and implementing effective change. J Hosp Infect. 2014;86(3):161-8. doi: 10.1016/j.jhin.2013.12.006.
  9. Borg MA, Cookson BD, Rasslan O, Gür D, Ben Redjeb S, Benbachir M, et al. Correlation between meticillin-resistant Staphylococcus aureus prevalence and infection control initiatives within southern and eastern Mediterranean hospitals. J Hosp Infect. 2009;71(1):36-42. doi: 10.1016/j.jhin.2008.09.007.
  10. Taguchi F1, Saito-Taki T, Okuda S, Aoki M, Matsuzaki T, Tomioka M, et al. [Proposal for the nosocomial infection control of methicillin-resistant Staphylococcus aureus (MRSA)]. Nihon Saikingaku Zasshi. 1992;47(6):767-75. Japonés.
  11. Instituto Mexicano del Seguro Social. Sistema de Vigilancia de Infecciones Nosocomiales de la Coordinación de Vigilancia Epidemiológica del Instituto Mexicano del Seguro Social. México: IMSS; 2013.
  12. Witte W, Braulke C, Heuck D, Cuny C. Analysis of nosocomial outbreaks with multiply and methicillin-resistant Staphylococcus aureus (MRSA) in Germany: implications for hospital hygiene. Infection. 1994;22 Suppl 2:S128-34.
  13. Moine P, Fish DN. Pharmacodynamic modelling of intravenous antibiotic prophylaxis in elective colorectal surgery. Int J Antimicrob Agents. 2013;41(2):167-73. doi: 10.1016/j.ijantimicag.2012.09.017.
  14. Wilson SE. Microbial sealing: a new approach to reducing contamination. J Hosp Infect. 2008 Nov;70 Suppl 2:11-4. doi: 10.1016/S0195-6701(08)60018-3.
  15. Zamudio-Lugo I, Meza-Chávez A, Martínez-Sánchez Y, Miranda-Novales MG, Espinosa-Vital JG, Rodríguez-Sing R. Estudio multimodal de higiene de manos en un hospital pediátrico de tercer nivel. Bol Med Hosp Infant Mex. 2012 Sep-Oct;69(5):384-90.
  16. Anaya-Flores VE, Ortiz-López S, Hernández-Zárate VE, García-Hernández A, Jiménez-Bravo ML, Ángeles-Garay U. Prevalencia de lavado de manos y factores asociados al incumplimiento. Estudio de sombra. Rev Enferm Inst Mex Seguro Soc. 2007; 15(3):141-6.
  17. Kotsanas D, Wijesooriya WR, Korman TM, Gillespie EE, Wright L, Snook K, et al. “Down the drain”: carbapenem-resistant bacteria in intensive care unit patients and handwashing sinks. Med J Aust. 2013 Mar 18;198(5):267-9.
  18. Roux D, Aubier B, Cochard H, Quentin R, van der Mee-Marquet N; HAI Prevention Group of the Réseau des Hygiénistes du Centre. Contaminated sinks in intensive care units: an underestimated source of extended-spectrum beta-lactamase-producing Enterobacteriaceae in the patient environment. J Hosp Infect. 2013 Oct;85(2):106-11. doi: 10.1016/j.jhin.2013.07.006.

Conflict of interest statement: The authors have completed and submitted the form translated into Spanish for the declaration of potential conflicts of interest of the International Committee of Medical Journal Editors, and none were reported in relation to this article.

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