Encuesta

The H1N1 epidemic caused an increase in consultations and admissions that peaked in November 2009. In particular the confrontation with resuscitations of young, previously healthy children in the home setting caused concerns. This led to a low threshold for admission of children <5 years of age with the suspicion of H1N1 infection. In retrospect the severity of disease due to H1N1 was relatively mild, although there are some notable observational done.

Table 3.3 Clinical symptoms at presentation of children admitted with an suspected H1N1 infection Admitted n = 61 (%) H1N1 + n= 24 (%) H1N1 - n = 37 (%) Fever 46 (75%) 20 (83%) 26 (70%)

Fever and respiratory symptoms 32 (52%) 15 (63%) 17 (46%)

Cough 31 (51%) 17 (71%) 14 (38%)

Gastrointestinal symptoms 10 (16%) 10 (42%) 4 (11%)

Vomiting 7 (12%) 5 (21%) 2 (5%)

Diarrhoea 12 (20%) 9 (38%) 3 (8%)

Respiratory / circulatory failure 8 (13%) 7 (29%) 1 (3%) Fever without respiratory symptoms 6 (10%) 2 (8%) 4 (11%)

laryngitis subglottica 5 (8%) 1 (4%) 4 (11%)

Upper Respiratory symptoms 1 (2%) 0 (0%) 1 (3%)

3

Of all admitted children with a H1N1 infection the majority were older than 5 years of age (17 of the 24 children, 71%) and it was especially in this age group that there was a serious course of disease (8 of the 17 children, 47%). A Canadian study in which 58 children with H1N1 infection are described, shows a similar distribution in terms of age distribution and severity of disease. Sixty-four percent of the children with H1N1 infection was older than 5 year, a significant difference with respect to the children who were

before them in 5 years recorded with a seasonal Influenza A infection.18 _{Initial reports}

from the United Kingdom show a similar distribution, where 12 of the 13 children who

were included in intensive care with H1N1 was older than 5 years of age. 9,11

The Dutch data collected by the National Institute for public health and the environment (RIVM) showed that the number of admissions per 100,000 is highest for the age group

0 to 5 years (62.7).1,2,7 _{The proportion of children under 6 months of age in this whole}

group is 33%. This percentage might be positively influenced by the advise to admit children <3 months during treatment with Oseltamivir. The number of admissions to intensive care units per 100,000 for the age group 0-5 years is equal to the number of ICU admissions for 5 to 14 years old (1.73 and 1.71, respectively) while the mortality in the youngest age category is higher per 100,000 (0.54 vs. 0.45, respectively). When we look at absolute numbers, more young children from 0 -4 years (581 vs. 384) were admitted to the hospital, but twice as many children aged 5 to 14 years needed admission to the ICU (32 vs. 16). Finally more children deceased in the age group 5 to

14 years (9 vs. 5).1,2,7

A number of exceptionally serious manifestations of H1N1 infections in previously healthy children were observed. Two children needed to be resuscitated at home, another arrived in circulatory shock at the emergency room. These three children were all 3 years old or younger, and represented 43% of all admitted children in the age group < 5 years of age; the other children from this age group (n = 4) were only admitted for observational purposes. In the study of Libster et al. a death rate of 5% is found this is significantly lower than the 17% mortality rate in our population. The number of ICU admissions (33 versus 19%) and the number of children that needed mechanical

ventilation (23 versus 17%) is also higher in our population.10 _{Miroballi et al. showed a}

similar rate of ICU admissions in New York, but they described a lower percentage of

mechanical ventilated children and a lower mortality rate of 1%. 14 _{This might be due to}

the academic setting of the hospital resulting in a bias that results in more children with significant comorbidity. Further the hospital functions as tertiary referral centre for the region.

The incidence of fever (83%) and cough (71%) as presenting symptoms of H1N1 infections in children is similar to the symptoms found in the literature (respectively

84-92% and 69-91%).9,10,19

However, there are also striking differences between our study and previously published studies concerning the presence of rhinitis and upper respiratory tract symptoms (ranging from 31-77% vs. 0% in our study group) and the occurrence of gastro-intestinal

Chapter 3

The influence of co-infections in the course of disease and the outcome is not yet clear. Libster et al. mention a (suspected) bacterial pneumonia in 10% of the children with a H1N1 infection, of which 16% developed an empyema. In 7% of the tested children (n = 147) a positive blood culture was found and 19% had a viral co-infection, usually RSV (89%).

Four children with a proven co-infection deceased in this group.10 _{Miroballi et al. found}

no viral co-infections and 3.5% bacterial co-infections. 14 _{These two studies show no}

increase in mortality based on the presence of a co-infection.10,14

In our study, children with H1N1 infections were not routinely tested for co-infections. Ultimately, 63% of the hospitalized children were tested for co-infections. The choice to perform diagnostics in children was based on the clinical parameters of the individual patient. Seventy-five percent of the patients with a severe course of disease had a viral or bacterial co-infection, also in 2 of the 4 deceased children a co-infection was demonstrated. Based on these small number of patients it is not possible to make a statement about the impact of co-infections in the course of disease.

Underlying medical conditions are a main risk factor for hospitalization and death due to influenza infections. Over 70% of the admitted children with a H1N1 infection had an underlying disease (chronic lung disease, immune deficiency, cardiac and neurological diseases). Other studies published lower percentages (40.3% and 34%) of underlying

diseases in comparable paediatric populations.9,11 _{The function of our hospital as a}

tertiary referral centre as previously mentioned might explain the differences in the percentage of children with an underlying medical condition. In our study there was no difference in mortality observed in patients with and without an underlying disorder. Fifty percent (2 out of 4 deceased children) had an underlying condition. In an Argentine study the presence of a complex underlying disease was significantly more frequent in

a group of children who died due to an H1N1 infection in the intensive care.20