Severe Pneumonia and Pandemic (H1N1) 2009, Mexico | CDC EID

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Volume 16, Number 1–January 2010
Research
Severe Pneumonia Associated with Pandemic (H1N1) 2009 Outbreak, San Luis Potosí, Mexico
Alejandro Gómez-Gómez, Martin Magaña-Aquino, Christian A. García-Sepúlveda, Uciel R. Ochoa-Pérez, Reynaldo Falcón-Escobedo, Andreu Comas-García, Saray Aranda-Romo, Hugo I. Contreras-Treviño, Paulina V. Jiménez-Rico, Mario A. Banda-Barbosa, Félix Dominguez-Paulin, J. Mario Bernal-Blanco, Luis F. Pérez-González, and Daniel E. Noyola
Author affiliations: Hospital Central "Dr. Ignacio Morones Prieto," San Luis Potosí, Mexico (A. Gómez-Gómez, M. Magaña-Aquino, R. Falcón-Escobedo, J.M. Bernal-Blanco, L.F. Pérez-González); Universidad Autónoma de San Luis Potosí, San Luis Potosí (A. Gómez-Gómez, M. Magaña-Aquino, C.A. García-Sepúlveda, U.R. Ochoa-Pérez, R. Falcón-Escobedo, A. Comas-García, S. Aranda-Romo, H.I. Contreras-Treviño, P.V. Jiménez-Rico, M.A. Banda-Barbosa, F. Dominguez-Paulin, J.M. Bernal-Blanco, L.F. Pérez-González, D.E. Noyola); and Servicios de Salud del Estado de San Luis Potosí, San Luis Potosí (U.R. Ochoa-Pérez)

Suggested citation for this article

Abstract
We describe the clinical characteristics and outcomes of adults hospitalized with pneumonia during the pandemic (H1N1) 2009 outbreak. Patients admitted to a general hospital in San Luis Potosí, Mexico, from April 10 through May 11, 2009, suspected to have influenza virus–associated pneumonia were evaluated. We identified 50 patients with suspected influenza pneumonia; the presence of influenza virus was confirmed in 18: 11 with pandemic (H1N1) 2009 virus, 5 with unsubtypeable influenza A virus, 1 with seasonal influenza A virus (H3N2), and 1 in whom assay results for seasonal and pandemic (H1N1) 2009 viruses were positive. Eighteen patients were treated in the intensive care unit, and 10 died. During the pandemic (H1N1) 2009 outbreak, severe pneumonia developed in young adults who had no identifiable risk factors; early diagnosis and treatment of influenza virus infections may have a determinant role in outcome.

A novel influenza A virus, pandemic (H1N1) 2009 virus, has been identified as the cause of an epidemic outbreak of respiratory illness throughout the world (1). Current information indicates that the pandemic (H1N1) 2009 virus has been circulating in Mexico since at least March 2009 and that it has been the cause of an increase in the number of hospitalizations of young adults since April 2009 (1). The city of San Luis Potosí played a major role in raising awareness of the presence of an unusual and nonsubtypeable influenza A virus during the early days of the outbreak (2).

The Hospital Central "Dr. Ignacio Morones Prieto" is a public hospital located in San Luis Potosí that served as a reference center for evaluation and treatment of patients with suspected influenza virus pneumonia. In this article, we describe the results of investigations performed to determine the etiology of this outbreak and report the clinical findings, treatments, and patient outcomes.

Patients and Methods
Study Site
The city of San Luis Potosí is located in central Mexico and is the capital of the state of San Luis Potosí (3). The state population was 2,410,414 in 2005; the population of the San Luis Potosí metropolitan area in the same year was 957,753 (4). The Hospital Central provides medical services to mid- and low-income populations from all areas of the state; it has 269 beds in total, 250 in adult and pediatric wards and 19 in the intensive care unit (ICU).

Patients
Starting April 10, 2009, when the first case of pandemic (H1N1) 2009 was identified, all patients admitted to Hospital Central with lower respiratory tract infections (LRTIs) were screened for the presence of influenza virus. Patients who experienced acute onset of respiratory symptoms (cough, rhinorrhea, and/or dyspnea) and fever were assessed for possible influenza-related pneumonia, including radiologic evaluation. This report includes all adult patients with radiographic evidence of pneumonia admitted during the first month of the pandemic (H1N1) 2009 outbreak.

Clinical, Laboratory, and Bacteriologic Information
Patients admitted to medical wards and the ICU were subjected to the hospital's standard diagnostic protocol: blood cultures, HIV antibody testing, chest radiograph, laboratory tests, and spontaneous or induced sputum samples for Gram staining and culture. These tests were performed at admission and every 48–72 hours thereafter. Patients receiving mechanical ventilation had samples for minibronchoalveolar lavage (mini-BAL) (5), blood, and urine sent for bacterial cultures at admission and every 48–72 hours, or in the event of new or persistent fever. Bronchoscopy with BAL was performed as clinically indicated. A quantitative threshold of 105 CFU/mL for mini-BAL was used and of 104 CFU/mL for BAL (6). Patients were treated with at least the following standard antimicrobial drug regimens: those with criteria for acute lung injury (ALI, partial pressure of oxygen in arterial blood [paO2]/fraction of inspired oxygen [FiO2] = 201–300) or acute respiratory distress syndrome (ARDS, paO2/FiO2<200) received ceftriaxone and/or vancomycin plus levofloxacin or clarithromycin, and patients treated in medical wards received levofloxacin. Therapeutic decisions were individualized by the attending physician. Deceased patients for whom the family granted consent were subjected to postmortem examinations to recover lung specimens for bacteriologic culture, influenza virus detection, and histopathologic analysis.

Sample Collection and Processing
Respiratory samples obtained from patients with suspected influenza infection were placed in either normal saline or viral transport media and kept refrigerated at 4°C until their arrival at the laboratory. A 200-μL aliquot of these samples was used for RNA extraction, and the remaining volume was stored at –70°C. Viral RNA was isolated using the High Pure Viral RNA Kit (Roche Diagnostics, Mannheim, Germany). Sample collection and processing were carried out according to national and international biosafety guidelines and recommendations (7,8).

Influenza Virus Detection
A multiplex reverse transcription–PCR (RT-PCR) capable of distinguishing type A from type B influenza virus was developed based on previously published primers (9). One-step RT-PCR was performed using the Access RT-PCR System (Promega Corporation, Madison, WI, USA) at 48°C for 45 min, followed by 94°C for 2 min, 40 cycles of 30 s at 94°C, 30 s at 56°C, and 30 s at 72°C, and a final step at 72°C for 5 min. Influenza A samples were subsequently subtyped using a multiplex PCR with sequence specific primers approach adapted from previous publications (Table 1) (11). PCR products were subjected to electrophoresis on 1.5% agarose gels prestained with ethidium bromide at 6 volts/cm for 45 min and digitally documented. An RT-PCR for detection of pandemic (H1N1) 2009 virus was developed based on early sequencing data (EpiFlu Database, http://platform.gisaid.org). RT was carried out at 38°C for 45 min by using UniFlu-RT oligonucleotide; PCR involved the newly developed Sw-NS-F 5´-ATG-GAC-TCC-AAC-ACC-3´ and Sw-NS-R 5´-TTA-AAT-AAG-CTG-AAA-CGA-G-3´ oligonucleotides at 1.6 μmol/L final concentration, 0.02 IU/μL of Taq (Vivantis Technologies Sdn Bhd Selangor D.E., Malaysia), 200 μmol/L deoxynucleoside triphosates, and 1.5 mmol/L MgCl2. PCR program was 95°C for 5 min, followed by 15 cycles of 95°C for 20 s, 54°C for 30 s, and 72°C for 1.5 min, and a final step of 2 min at 72°C. One microliter of a 1:1 dilution of the first PCR product was then used in a second PCR by using similar components except 1 mmol/L MgCl2 and 800 nmol/L final concentration of internal oligonucleotides Sw1-F 5´-CTT-GAA-AGA-GGA-ATC-GAG-CG-3´ and Sw1-R 5´-GTC-TCC-CAT-TCT-CAT-CAC-AGT-3´ (429-bp amplicon). Influenza virus detection at the Instituto de Diagnóstico y Referencia Epidemiológicos (InDRE) and the State Public Health Laboratory used the real-time RT-PCR protocol developed by the US Centers for Disease Control and Prevention (CDC).

Virologic and Epidemiologic Data
To assess the presence of respiratory syncytial virus (RSV) and influenza in the community, we reviewed the database at the Virology Laboratory Universidad Autónoma de San Luis Potosí (UASLP) and recorded the weekly number of viral detections from January 2008 through May 2009. In addition, the weekly number of acute respiratory infections (ARI) reported in the state of San Luis Potosí and the emergency department (ED) at the Hospital Central was recorded.

Statistical Analysis
We analyzed demographic and clinical characteristics using descriptive statistics. Means or medians were used for description of continuous variables according to data distribution; categorical variables were described with the use of percentages. Comparisons among patient groups were made to assess factors associated with severe infections. We compared categorical variables using the χ2 or Fisher exact test; continuous variables were compared by using the Student t test or Mann-Whitney U test, according to data distribution. A p value <0.05 was considered significant. Statistical analyses were performed with SPSS for Windows (version 14.0, SPSS Inc., Chicago, IL, USA).

Suggested Citation for this Article
Gómez-Gómez A, Magaña-Aquino M, García-Sepúlveda CA, Ochoa-Pérez UR, Falcón-Escobedo R, Comas-García A, et al. Severe pneumonia associated with pandemic (H1N1) 2009 outbreak, San Luis Potosí, Mexico. Emerg Infect Dis [serial on the Internet]. 2010 Jan [date cited]. Available from http://www.cdc.gov/EID/content/16/1/27.htm

DOI: 10.3201/eid1601.090941

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