Intra-Familial T ransmission of Influenza A and Influenza B

[mixin]

Conclusions:
The secondary infection rate in households is significantly
high: 9.6% for the A virus and 9.8% for B. The key to containing
influenza outbreaks, therefore, is preventing children from both
contracting and spreading the virus. The results of this study
also may be useful for determining who should be given priority
in the administration of anti-influenza drugs when supplies are
limited.

Discussion:
The incidence of influenza in one community during a fiveyear
period was 4.3% for influenza A and 2.7 % for influenza
B. However, when the virus spread in families, the incidence
rose to 9.6% for influenza A and to 9.8% for influenza B. The
incidence rate of intra-familial infection was 21.7% for influenza
A and 21.3% for influenza B. The family infection rates were two
or three times higher than the general infection rate. Secondary
infection in families was particularly high when the index cases
were children under age seven. The infection rate in such cases
was higher than 11%, suggesting that the virus survives longer
in small children than in adults. In our previous examination,
we observed the number of patients with detectable viruses
among children under 16 compared to people 16 years or
older, including parents. In people 16 years or older, the virus
was completely gone 5.5 days after onset, whereas for those
under 16 it took more than 6.5 days. The figures substantiated
that children are major contributors to the spread of influenza.
The average interval between the onset of an index case and
secondary infection was 2.57 days for influenza A and 3.54 days
for influenza B. The B virus has been shown in other studies to
survive longer than the A virus.[1] The result is substantiated by
the fact that the influenza A virus of our study survived in 50 %
of the patients for 3.5 days after onset and the influenza B virus
survived for 4.5 days.

http://www.isirv.org/media/pdf/OptionsVI_proceedings.pdf

[gsgs]

Re: Intra-Familial T ransmission of Influenza A and Influenza B

> The incidence of influenza in one community during a fiveyear
> period was 4.3% for influenza A and 2.7 % for influenza B.

per year ? 4.3% of people in that community had flu-A per year/season ?

> However, when the virus spread in families, the incidence
> rose to 9.6% for influenza A and to 9.8% for influenza B.

and ? Did it spread in families ?

> The incidence rate of intra-familial infection was 21.7% for influenza
> A and 21.3% for influenza B.

I don't understand these subtle differences.

I remember that I earlier saw a ~20% chance to become infected
when a family member is infected.
That was surprisingly low, lower than for colds

[mixin]

Re: Intra-Familial T ransmission of Influenza A and Influenza B

These OptionsVI studies are really long...I can post the whole studies if anyone wants them? There are also a lot of charts and graphs I can't see with this download.

Here's more:
We studied 1,636 flu cases in the last five influenza seasons, all confirmed by a positive result by rapid diagnostic test kit.

Results
Attack rate and recurrent attack rate by age group over the five flu
seasons. Overall, 30.7% of all groups became infected with either
influenza A or B. Of those, 19.8% were infected more than once.
The infection rate among children aged 4 to 6 years old was
59.7%. Of them, 33.3%, or 19.9% of the total, were infected more
than once. The infection rate among children aged 7 to 12 was
55.1% and the percent who caught influenza more than once
among this age group was 28.8%, which is high for children.

1,636 flu patients from 1,255 families were tracked over the
last 5 seasons. Of these families, 381, or 30.4%, had multiple
infections. 983 people from 754 families were infected with
influenza A. Of them, 229 families had multiple infections. 626
people from 477 families were infected with influenza B. Of
those families, 149 had multiple infections. The influenza type
of 26 patients from the 2001/2002 season are unknown because
the use of rapid test kits other than Capilia prevented us from
distinguishing between the A virus and B virus. The precise data
for one patient from the 2003/2004 season is also unknown
because the patient tested positive for both Capilia A and B.

Incidence rate of intra-familial infection and the families? infection
rate in intra-familial infection. Intra-familial infection by influenza
A and B was determined for families comprised of two to eight
members. The number of four member families with influenza
A was 360, or about half of the 756 families we monitored. The
next largest in number was three-member families, at 224,
followed by five-member families at 112. Families of up to five
members accounted for 95.5% of the total. Influenza B affected
484 families ranging from two members to seven. As in the case
of influenza A, families with four members accounted for about
half of the total, or 235 families, followed by 123 three-member
families and 70 five-member families. Secondary infection with
influenza A did not occur in two-member families. It occurred
in 43 three-member families, this is 19.2% of the inter-familial
infection; 22.5% was in four-member families and 25.0% in fivemember
families. As the figures indicate, the larger the family,
the more likely it was to suffer secondary infection. In all, 164
families, or 21.7%, suffered secondary infections. Secondary
infections of influenza B occurred in 7.9% of two-member
families, 13% of three-member families and 22.6% of fourmember
families. As the figures indicate, the larger the family,
the more likely it was to suffer secondary infection. In all, 103
families, or 21.3% of the total, had secondary infections. This
trend is similar to that for influenza A. Next, we observed the
number of family members with influenza A and B exposed to
influenza viruses by index cases in respective families and the
number of family members infected by the index case (or the
family infection rates). Among families that suffered secondary
infections of influenza A, about 10% suffered further spread
of the disease. The number of secondary infections rose with
larger families but the rate of infection stayed the same. The
percentage of people with influenza B who suffered secondary
infection was especially high in five-member families, at 14.3%,
but the overall secondary infection rate of the B virus was 9.8%,
a level similar to that for influenza A (Table 1).

Incidence rate of inter-familial infection and the family infection
rate in inter-familial infection by index case age. Table 1 shows
familial infection of influenza based on an index case in each
family. Index cases included grandparents, fathers, mothers,
and children. Child index cases were further classified into five
age groups: zero to three years, four to six, seven to nine, ten
to twelve, and 13 and older. With influenza A, among children
under age four who were infected first, 28.3% infected other
family members. For children four to six years old, the figure was
31.7%. Children under seven were highly likely to pass on their
infections to family members. The overall rate of secondary
infection was 21.7%. Among index cases, 9.6% passed the virus
to family members. When index cases were children under four,
the infection rate was 13.6%. For those aged four to six, the
rate was 13.3%. For familial infection of influenza B based on
an index case in each family, the 484 index cases included 337
children, or 69.6% of all index cases. The overall incidence rate
of inter-familial infection was 21.3% ? a level similar to that for
influenza A. Among children under 12 who were infected first,
23.0 to 27.6% infected other family members. In the case of
mothers who were index cases, the secondary infection rate was
also high, at 23.5%. The overall family infection rate was 9.8%
? a level similar to that for influenza A. But unlike influenza A,
there were no significant differences in the secondary infection
rates for the age groups under the age of 12, and the rates of
influenza B infection from mothers was also high, suggesting
that relatively older members of families are also likely to spread
the virus.

[gsgs]

Re: Intra-Familial T ransmission of Influenza A and Influenza B

I don't like the way how they express themselves.


>We studied 1,636 flu cases in the last five influenza seasons,
>all confirmed by a positive result by rapid diagnostic test kit.

they just picked the flu-cases from the tests or they had
observed a larger group and there were 1636 flu cases among them ?

>Results
>Attack rate and recurrent attack rate by age group over the five flu
>seasons.

this seems to imply a larger group (also healthy ones) of observants.
However they don't say how many (?)

>Overall, 30.7% of all groups

presumably they mean :
30.7% of the people had at least one episode of flu

>became infected with either
>influenza A or B. Of those, 19.8% were infected more than once.

no flu: 69.3%
one flu : 24.6%
2 or more flus: 6.1%

>The infection rate among children aged 4 to 6 years old was

"infection rate", is the percentage within the group who
had at least one flu in the 5 years. So 30.7% in the supergroup
of all people.

>59.7%. Of them, 33.3%, or 19.9% of the total, were infected more
>than once.

4-6 group:
no flu: 40.3%
one flu: 39.8%
2 or more flus: 19.9%

>The infection rate among children aged 7 to 12 was
>55.1% and the percent who caught influenza more than once
>among this age group was 28.8%, which is high for children.

7-12 group:
no flu:44.9%
one flu:39.2%
2 or more flus:15.9%

>1,636 flu patients from 1,255 families were tracked over the
>last 5 seasons.

how did they know in advance, who would be flu-patient ?
They must have tracked ~5000 people and later picked
those who had had flu

>Of these families, 381, or 30.4%, had multiple
>infections.

influenza-infections ? At least 2 episodes of flu within the
5 years in the family ?

>983 people from 754 families were infected with
>influenza A.
>Of them, 229 families had multiple infections. 626
>people from 477 families were infected with influenza B. Of
>those families, 149 had multiple infections. The influenza type
>of 26 patients from the 2001/2002 season are unknown because
>the use of rapid test kits other than Capilia prevented us from
>distinguishing between the A virus and B virus. The precise data
>for one patient from the 2003/2004 season is also unknown
>because the patient tested positive for both Capilia A and B.

just omit those (don't bother us with the details, adapt
the statistics so it reflects the situation best)

>Incidence rate of intra-familial infection and the families infection
>rate in intra-familial infection. [headline]
>Intra-familial infection by influenza
>A and B was determined for families comprised of two to eight
>members.

intra-familial infection rate for falilies with 1 member is 0.
there were no families with more than 8 members ?

>The number of four member families with influenza
>A was 360, or about half of the 756 families we monitored.

only 756 families were monitored and all of them had at least
one flu-episode ?

>The next largest in number was three-member families, at 224,
>followed by five-member families at 112. Families of up to five
>members accounted for 95.5% of the total. Influenza B affected
>484 families ranging from two members to seven. As in the case
>of influenza A, families with four members accounted for about
>half of the total, or 235 families, followed by 123 three-member
>families and 70 five-member families. Secondary infection with
>influenza A did not occur in two-member families. It occurred
>in 43 three-member families, this is 19.2% of the inter-familial
>infection; 22.5% was in four-member families and 25.0% in fivemember
>families. As the figures indicate, the larger the family,
>the more likely it was to suffer secondary infection. In all, 164
>families, or 21.7%, suffered secondary infections. Secondary
>infections of influenza B occurred in 7.9% of two-member
>families, 13% of three-member families and 22.6% of fourmember
>families. As the figures indicate, the larger the family,
>the more likely it was to suffer secondary infection. In all, 103
>families, or 21.3% of the total, had secondary infections. This
>trend is similar to that for influenza A. Next, we observed the
>number of family members with influenza A and B exposed to
>influenza viruses by index cases in respective families and the
>number of family members infected by the index case (or the
>family infection rates). Among families that suffered secondary
>infections of influenza A, about 10% suffered further spread
>of the disease. The number of secondary infections rose with
>larger families but the rate of infection stayed the same. The
>percentage of people with influenza B who suffered secondary
>infection was especially high in five-member families, at 14.3%,
>but the overall secondary infection rate of the B virus was 9.8%,
>a level similar to that for influenza A (Table 1).

ahh, a table ! That should be easier to grasp than the story
which they made of it.
Let me see if I can find the table, cause this back-translation
of text to table takes so much time



>Incidence rate of inter-familial infection and the family infection
>rate in inter-familial infection by index case age. Table 1 shows
>familial infection of influenza based on an index case in each
>family. Index cases included grandparents, fathers, mothers,
>and children. Child index cases were further classified into five
>age groups: zero to three years, four to six, seven to nine, ten
>to twelve, and 13 and older. With influenza A, among children
>under age four who were infected first, 28.3% infected other
>family members. For children four to six years old, the figure was
>31.7%. Children under seven were highly likely to pass on their
>infections to family members. The overall rate of secondary
>infection was 21.7%. Among index cases, 9.6% passed the virus
>to family members. When index cases were children under four,
>the infection rate was 13.6%. For those aged four to six, the
>rate was 13.3%. For familial infection of influenza B based on
>an index case in each family, the 484 index cases included 337
>children, or 69.6% of all index cases. The overall incidence rate
>of inter-familial infection was 21.3% – a level similar to that for
>influenza A. Among children under 12 who were infected first,
>23.0 to 27.6% infected other family members. In the case of
>mothers who were index cases, the secondary infection rate was
>also high, at 23.5%. The overall family infection rate was 9.8%
>– a level similar to that for influenza A. But unlike influenza A,
>there were no significant differences in the secondary infection
>rates for the age groups under the age of 12, and the rates of
>influenza B infection from mothers was also high, suggesting
>that relatively older members of families are also likely to spread
>the virus.

[gsgs]

Re: Intra-Familial T ransmission of Influenza A and Influenza B

table 1
incidence rate of intra-familial infection
and the families' infection rate in intra-familial infection

(0) members in family
(1) No.of families
(2) No. of families with secondary infection
(3) % of families with secondary infection
(4) No. of observed family members
(5) No. of infected members
(6) % of infected members
(7) age of index case
(8) influenza subtype

8  0   1   2    3    4   5    6
----------------------------------
A  2  26   0  0.0   26   0  0.0
A  3 224  43 19.2  448  47 10.5
A  4 360  81 22.5 1080 109 10.1
A  5 112  28 25.0  448  37  8.3
A  6  25   8 32.0  125  13 10.4
A  7   7   3 42.9   42   3  7.1
A  8   2   1 50.0   14   1  7.1
B  2  38   3  7.9   38   3  7.9
B  3 123  16 13.0  246  18  7.3
B  4 235  53 22.6  705  65  9.2
B  5  70  26 37.1  280  40 14.3
B  6  14   3 21.4   70   5  7.1
B  7   4   2 50.0   24   2  8.3
B  8   0   0  0.0    0   0  0.0

8      7    1   2    3    4   5    6
------------------------------------
A   0- 3  113  32 28.3  301  41 13.6
A   4- 6  123  39 31.7  368  49 13.3
A   7- 9   83  20 24.1  256  24  9.4
A  10-12   99  20 20.2  302  31 10.3
A  >12    146  21 14.4  434  25  5.8
A  moms   107  15 14.0  284  18  6.3
A  dads    82  16 19.5  226  21  9.3
A  gr.p     3   1 33.3   12   1  8.3
B   0- 3   47  11 23.4  124  14 11.3
B   4- 6  105  29 27.6  312  36 11.5
B   7- 9   74  17 23.0  230  24 10.4
B  10-12   38   9 23.7  121  13 10.7
B  >12     73   8 11.0  215  11  5.1
B  moms    81  19 23.5  194  22 11.3
B  dads    61   9 14.8  151  13  8.6
B  gr.p     5   1 20.0   16   1  6.3

[gsgs]

Re: Intra-Familial T ransmission of Influenza A and Influenza B

my summary : once some member of your family has the flu,
then there is a 10% chance that you'll get it too.

83% of intra-familial infections happen in the first 5 days,
100% in the first 14 days.