2015 HSC Section 1 Book of Articles

United States but only a nonsig-

cant reduction in con

rmed hos-

pitalization events in children aged

1 year. In contrast, a recent study

from the United States showed a sus-

tained decrease in hospitalizations

for pneumonia in children and a de-

crease in people

65 years old, pos-

sibly a herd effect.

Our use of

a discharge diagnosis of pneumonia

coded as bacterial pneumonia as an

endpoint was motivated by the dif

culty of establishing an etiological

diagnosis of pneumonia, especially in

small children.

Interestingly, we observed an in-

creasing incidence of admissions to

the hospital for pneumonia among

children

2 years and from 5 to

years old before vaccine introduction,

from 2003 to 2007 (Fig 1). The reason

for this increase is unclear, but nat-

ural

uctuations caused by expansion

of certain pneumococcal serotypes or

clones might have contributed. A

similar increase in 2004 to 2006 was

seen in a national time trend (1997 to

2008) study on hospitalizations for

pneumonia among children in England.

This might have led to an underes-

timation of the real effect of the PCV

vaccination, because we did not cal-

culate expected rates assuming a

continued increasing trend and com-

paring those with the observed rates,

as was done in other studies.

Previous in

uenza virus infection has

been shown to increase the risk of

developing pneumococcal pneumo-

nia.

28,29

Recent data from the United

States showed excess risk of pneu-

mococcal pneumonia during the H1N1

uenza pandemic in 2009.

In our

study we observed only an increase

in hospitalizations for pneumonia,

coded as bacterial pneumonia, in

children aged 2 to

5 years during

this pandemic. There was a high cov-

erage rate (50% of children aged 6

months to 2 years, 70% of children

TABLE 2

Trend Analysis of Monthly Hospitalizations by Discharge Diagnosis per 100 000 Person-Years by Age Group in Stockholm County, Sweden, 2003

–

2012

Disease (Age Group)

RR (95% CI)

Disease (Age Group)

RR (95% CI)

Disease (Age Group)

RR (95% CI)

Sinusitis (0

–

2 y)

Sinusitis (2

–

5 y)

Sinusitis (5

–

18 y)

Preintervention trend

1.00 (0.992

–

1.017)

.47

Preintervention trend

1.01 (0.991

–

1.029)

.32

Preintervention trend

1.01 (0.996

–

1.029)

.13

Change in level

0.52 (0.265

–

1.014)

.055

Change in level

1.026 (0.434

–

2.425)

.95

Change in level

0.77 (0.381

–

1.561)

.47

Postintervention trend

0.976 (0.957

–

0.996)

.018

Postintervention trend

0.969 (0.949

–

0.990)

.004

Postintervention trend

1.00 (0.985

–

1.014)

.96

Pneumonia (0

–

2 y)

Pneumonia (2

–

5 y)

Pneumonia (5

–

18 y)

Preintervention trend

1.01 (1.004

–

1.017)

.001

Preintervention trend

1.004 (0.997

–

1.011)

.29

Preintervention trend

1.01 (1.007

–

1.022)

.001

Change in level

0.65 (0.494

–

0.856)

.002

Change in level

0.90 (0.647

–

1.255)

.54

Change in level

0.50 (0.357

–

0.70)

.001

Postintervention trend

0.996 (0.990

–

1.001)

.13

Postintervention trend

0.992 (0.985

–

0.999)

.02

Postintervention trend

1.01 (1.005

–

1.019)

.001

Pyelonephritis (0

–

2 y)

Pyelonephritis (2

–

5 y)

Pyelonephritis (5

–

18 y)

Preintervention trend

1.00 (0.994

–

1.007)

.99

Preintervention trend

1.00 (0.990

–

1.016)

.67

Preintervention trend

1.003 (0.992

–

1.014)

.64

Change in level

1.09 (0.809

–

1.474)

.57

Change in level

0.974 (0.551

–

1.740)

.93

Change in level

1.123 (0.681

–

1.849)

.65

Postintervention trend

1.00 (0.994

–

1.006)

.90

Postintervention trend

0.999 (0.987

–

1.010)

.82

Postintervention trend

1.003 (0.994

–

1.013)

.52

When referring to the preintervention and postintervention trend, the RR expresses the month-to-month change in hospitalization rates. For the change in level it expresses comparison of the hospitalization rate of the

rst postintervention month to the

last preintervention one.

PEDIATRICS Volume 134, Number 6, December 2014

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