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30 Jul 2009

Eurosurveillance - Epidemiologic analysis of the laboratory-confirmed cases of influenza A(H1N1)v in Colombia

Eurosurveillance, Volume 14, Issue 30, 30 July 2009

Rapid communications

Epidemiologic analysis of the laboratory-confirmed cases of influenza A(H1N1)v in Colombia

M Á Castro-Jiménez 1,2, J O Castillo-Pabón 1, G J Rey-Benito 1, P A Pulido-Domínguez 1, J Barbosa-Ramírez 1, D A Velandia-Rodriguez 1, E S Angulo-Martínez 1, on behalf of the Virology Group and the Communicable Diseases Surveillance Group1
1. Instituto Nacional de Salud (National Institute of Health), Bogotá, Colombia
2. Grupo GUINDESS, Departamento de Salud Pública, Universidad Industrial de Santander, Bucaramanga, Colombia

Citation style for this article: Castro-Jiménez MÁ, Castillo-Pabón JO, Rey-Benito GJ, Pulido-Domínguez PA, Barbosa-Ramírez J, Velandia-Rodriguez DA, Angulo-Martínez ES, on behalf of the Virology Group and the Communicable Diseases Surveillance Group. Epidemiologic analysis of the laboratory-confirmed cases of influenza A(H1N1)v in Colombia. Euro Surveill. 2009;14(30):pii=19284. Available online: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19284

Date of submission: 22 July 2009


From 2 May to 16 July 2009, a total of 183 laboratory-confirmed cases of influenza A(H1N1)v were reported in Colombia, 117 (63.9%) of these had travelled outside the country. Hospital admission was necessary in 26 (14.21%) cases and seven patients died (fatality-case ratio: 3.8%). The infection affected younger age-groups and the symptoms most frequently reported were cough, fever and sore throat. Our findings are consistent with recent reports from other countries.


Background

Since the first human cases of influenza A(H1N1)v were identified in Mexico and the United States, a rapid spread of this infection has been observed across the world [1,2]. On 11 June 2009, the World Health Organization declared influenza pandemic [3]. On 24 April 2009, the Colombian public health authorities implemented the National Plan for Prevention and Control of Pandemic Influenza and they reported the first cases in travellers including a group of athletes returning from a sporting event in Orlando, United States. This paper describes the main demographic and clinical characteristics of the first cases of influenza A(H1N1)v in Colombia reported during the period from 2 May to 16 July, 2009.


Methods

A suspected case was initially defined as a patient with acute respiratory symptoms and a history of travel to Mexico, United States or any other affected country within seven days before the onset of symptoms or a history of close contact with a confirmed or probable case. However, this definition has been updated due to the rapid spread of infection and the presence of laboratory-confirmed cases in patients who had not travelled outside the country. The current definition of suspected case includes history of travel in any affected country or acute respiratory illness requiring hospitalisation. A probable case is defined as an individual with an acute febrile respiratory illness who is positive for influenza A but classified as undetermined for the new virus by using a specific Real Time-PCR (rRT-PCR) from CDC (protocol reference: I-007-005). A confirmed case is defined as a patient with acute respiratory symptoms who tested positive for influenza A(H1N1)v using the specific rRT-PCR. In a few patients, the presence of the virus was confirmed by gene sequencing [4,5].

Demographic, clinical, and epidemiologic data of patients meeting these criteria for surveillance were sent to the National System of Public Health Surveillance (SIVIGILA) by public and private hospitals. This information was validated using photocopies of the clinical records if they were available and face-to-face or telephone interviews of the patients (or their families) who were diagnosed as having the infection. Respiratory samples by throat swabs from patients with respiratory symptoms who had been defined as suspected cases of this virus were tested by rRT-PCR. In some of the patients who died, tissue samples (lung, trachea and bronchia) were also collected and analysed. Additionally, in a few patients, direct immunofluorescence (DIF) test has also been used in order to evaluate concomitant infection of other respiratory viruses such as seasonal influenza A or B virus, respiratory syncytial virus, parainfluenza virus (1, 2 and 3) and adenoviruses.

Categorical variables were presented as percentages and Pearson´s or Fisher's exact tests were employed to compare groups. Quantitative variables were statistically tested for the normality of distribution by using the Shapiro-Wilk test. A non-normal quantitative variable was summarised as median and interquartile range (IQR) and two median were compared using the Wilcoxon rank-sum test. P-values less than 0.05 were considered as statistically significant.


Results

On 2 May 2009, the first confirmed Colombian case of influenza A(H1N1)v was reported. By 16 July, 183 cases have been confirmed (including four cases confirmed by gene sequencing). Of these, 96 (52.4%) were men. The distribution of cases by week of onset of symptoms is shown in Figure 1. A history of travel outside the country was found in 117 (63.9%) patients, most of them had travelled to United States (n=71), Argentina (n=12), México (n=7) and Chile (n=7). In 65 (35.5%) confirmed cases there was no history of travel outside Colombia and for one patient this information was not available. The majority of cases were from the provinces of Bogotá, Valle, Antioquia and Atlántico.

[Figure 1. Number of laboratory-confirmed cases of influenza A(H1N1)v by week of onset and history of travel, Colombia, reported 2 May - 16 July 2009 (n=182*)]

The median age of cases was 27 years (IQR: 17-38). Cases ranged in age from 0 to 72 years and 80% of cases were aged less than 40 years. There were no differences in the median of age of cases by sex (women: 28 years; IQR: 18-39; men: 25 years, IQR: 16.5-36.5; p=0.24). The distribution of laboratory-confirmed cases of influenza A(H1N1)v by age group and history of travel is shown in Figure 2.

[Figure 2. Number of laboratory-confirmed cases of influenza A(H1N1)v by age group and history of travel, Colombia, reported 2 May - 16 July 2009 (n=182*)]

The clinical manifestations are listed in the Table. Headache and shortness of breath were observed more frequently in women than in men, but these differences were not significant. The symptoms most frequently reported included fever, cough, sore throat, nasal discharge and headache (n=78; 84.8%).

[Table. Distribution of laboratory-confirmed cases of influenza A(H1N1)v by sex and clinical manifestations, Colombia, reported May 2 - July 16 2009]

Twenty six patients (14.2%) were admitted to hospital because of complications. Patients who experienced shortness of breath were more likely to be hospitalised than those without this symptom (28.4% and 2.1%, respectively; p<0.001) while patients who reported headache were less likely to be hospitalised (p=0.031). Seven patients who were hospitalised died, including five women. Only two of the fatal cases had underlying medical conditions, including obesity (n=1) and underweight (n=1). The case-fatality ratio was 3.8%. The medical complications related to hospitalisation and deaths were acute respiratory failure, pneumonia, hypoxia, pneumothorax, acute tracheitis, tracheobronchitis and sepsis. No influenza A(H1N1)v-related deaths have been reported in pregnant women.

The analysis of the first eight cases who have also been tested for other respiratory viruses showed coinfection of influenza A(H1N1)v with parainfluenza type 1 and influenza B viruses in one patient, and with parainfluenza type 3 virus in another patient, while the remaining six were negative.


Discussion

Our results show that 35% of laboratory-confirmed cases had no history of travel outside the country which is an evidence of local transmission. Data also suggest that young people were affected more often than older people. It is very noticeable that the proportion of people younger than 40 years of age among the first 40 cases reported was the same as in the dataset analysed here (80%) but, in the rest of the cases, the infection has expanded the age range from 40-54 to 40-72 years.

The age distribution of cases was similar to that observed by researchers in other countries [6,7]. Our number of confirmed cases is relatively low and we were unable to find any significant differences between sexes. Clinical manifestations reported by our patients were similar to those described by other authors [7,8].

The majority of fatal cases had no underlying medical conditions. Obesity has recently been considered as a possible risk factor for severe disease [9]. This condition was found in one of the fatal cases. Finally, we considered that one reason for the relatively high case-fatality ratio observed in this dataset is that we took into account only the laboratory-confirmed cases.


Acknowledgements

The authors are thankful to Dr. Pilar Andrea Tavera-Rodríguez, Dr. Adriana Patricia Rodríguez-Cárdenas, Dr. Jose Alejandro Daza-Vergara and Dr. Helena Patricia Salas- Suspes for their valuable support.


References

1. World Health Organization (WHO). Swine influenza-Statement by WHO Director-General, Dr Margaret Chan. 2 May 2009. Available from: http://www.who.int/mediacentre/news/statements/2009/h1n1_20090427/en/index.htm
2. Centers for Disease Control and Prevention (CDC). Swine Influenza A(H1N1) infection in Two Children- Southern California, March-April 2009. MMWR Morb Mortal Wkly Rep. 2009;58. Available from: http://www.cdc.gov/mmwr/preview/mmwrhtml/mm58d0421a1.htm
3. World Health Organization (WHO). Influenza A (H1N1): WHO announces pandemic alert phase 6, of moderate severity. 12 June 2009. Available from: http://www.euro.who.int/mediacentre/PR/2009/20090611_1
4. Gómez LA, Gunturiz ML, Méndez JA, Rey GJ. Influenza A virus (A/Bogota/176/2009(H1N1)) segment 6 neuraminidase (NA) gene, partial cds. 22 July 2009. Available from: http://www.ncbi.nlm.nih.gov/nuccore/238018151?ordinalpos=1&itool=EntrezSystem2.PEntrez.Sequence.Sequence_ResultsPanel.Sequence_RVDocSum
5. Gunturiz ML, Méndez JA, Rey GJ, Gómez LA. Influenza A virus (A/Bogota/224/2009(H1N1)) segment 4 hemagglutinin (HA) gene, partial cds. 22 July 2009. Available from: http://www.ncbi.nlm.nih.gov/nuccore/238018155?log$=activity.
6. Novel Swine-Origin Influenza A (H1N1) Virus Investigation Team. Emergence of a Novel Swine-Origin Influenza A (H1N1) Virus in Humans. N Engl J Med. 2009; 360(25):2605-15.
7. New influenza A(H1N1) investigation teams. New influenza A(H1N1) virus infections in France, April – May 2009. Euro Surveill. 2009;14(21):pii=19221. Available from: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19221
8. Shimada T, Gu Y, Kamiya H, Komiya N, Odaira F, Sunagawa T, et al. Epidemiology of influenza A(H1N1) virus infection in Japan, May - June 2009. Euro Surveill. 2009;14(24):pii=19244. Available from: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19244
9. Centers for Disease Control and Prevention (CDC). Intensive-Care Patients With Severe Novel Influenza A (H1N1) Virus Infection --- Michigan, June 2009. MMWR Morb Mortal Wkly Rep. 2009;58. Available from: http://www.cdc.gov/mmwr/preview/mmwrhtml/mm58d0710a1.htm
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