Haemophilus influenzae

Background

Haemophilus influenzae (H. influenzae) are bacteria commonly carried in the respiratory tract, which can cause acute invasive disease. They are divided into encapsulated and unencapsulated (non-typeable) strains. Encapsulated strains can be classified into six serotypes, from a to f, of which type b (Hib) was most prevalent prior to vaccine introduction. Infection with H. influenzae can cause the following conditions:

  • meningitis
  • septicaemia
  • acute respiratory infections

Less frequent conditions which may be caused by H. influenzae infection include:

  • epiglottitis
  • osteomyelitis
  • septic arthritis

For more information on H. influenzae, visit the NHS inform website.

Guidance

Guidance on Haemophilus influenzae can be found below:

For all infection prevention and control guidance visit the A-Z ​pathogens section of the National Infection and Prevention Control Manual.

Data and surveillance

In 1992, following introduction of the Hib vaccine for young children, the number of H. influenzae type b cases fell dramatically, not only in the vaccinated group but also in older age groups.  Due to reduced carriage of the organism within the respiratory tract of vaccinated children, transmission to the wider community was effectively suppressed. The addition of the Hib booster vaccine in 2006, reduced case numbers further.

In Scotland, typing is conducted on  all cases with positive laboratory reports for H. influenzae, in order that national trends in disease subtypes can be monitored. Further enhanced surveillance is carried out for all H. influenzae cases identified in children under the age of 5 and type b strains across all age groups.

Surveillance update for April to June 2020

Nine cases of invasive H.influenzae were reported in the second quarter of 2020, bringing the total for January to June (weeks 1 to 26) to 32. This is lower than the cumulative case numbers reported for the same period in the previous four years (range 40 to 53), as shown in Figure 1.

Figure 1: Cumulative number of Haemophilus influenzae cases reported to HPS 2008 to 2020 (to week 26)

Figure 1 is a series of line graphs showing the cumulative number of Haemophilus influenzae cases reported to Health Protection Scotland per week by year. Each line represents a different year from 2016 to the end of the second quarter of 2020 and all years show a steady increase in cumulative number of cases per week. The number of cases so far in 2020 is lower than for the corresponding periods in the previous four years.

Of the 32 cases reported to the end of the second quarter of 2020:

  • two (6.3%) were aged under five years
  • one (3.1%) was aged between five and 20 years
  • five (15.6%) were aged between 21 and 40 years
  • 24 (75.0%) were over 40 years of age

Of the 32 invasive cases reported so far in 2020:

  • 28 (87.5%) had influenzae isolated from blood
  • two (6.3%) from cerebrospinal fluid
  • two (6.3%) from pleural fluid

There were no known deaths associated with H.influenzae to the end of the second quarter of 2020.

Figure 2 demonstrates the epidemiological impact of the Hib vaccine, for those aged under five (routinely vaccinated group) and for all ages (including under fives). There was a marked decrease in cases from 1992 in all age groups, followed by a rise in case numbers in the early 2000s. Case numbers decreased again following the introduction of the Hib booster vaccine, and figures have remained relatively stable since 2011.

Figure 2: Laboratory reports of invasive Haemophilus influenzae type b disease in Scotland, 1988 to 2020 (to week 26)

Figure 2 is a line graph showing the number of invasive Haemophilus influenzae type b disease cases reported to Health Protection Scotland from 1988 to the end of the second quarter of 2020. There are two lines on the graph, one representing the under 5 age group and the other, total number of cases (including under 5 years). Following introduction of the Hib vaccine in 1992, cases rapidly decreased to single figures. However, in 2001 a sharp increase was observed and total number of cases peaked at 31 in 2002, prompting introduction of the Hib booster campaign in June 2003. Cases across all ages subsequently decreased and following introduction of a routine Hib booster in 2006, reached low numbers by 2009. Only one case has been observed in the under 5 age group between 2011 and the end of the second quarter of 2020.

Figure 3 presents laboratory reports by serotype, since the introduction of the Hib booster campaign in 2003.

H. influenzae typing was carried out for 25 (78.1%) isolates, of which:

  • 21 (84.0%) were non-typeable (NT)
  • three (12.0%) were type f
  • one (4.0%) was type a

Figure 3: Laboratory reports of Haemophilus influenzae by serotype, 2003 to 2020 (to week 26)

Figure 3 is a bar chart showing the laboratory reports of Haemophilus influenzae by type from 2003 to the end of the second quarter of 2020. The chart shows a steady decline in type b infection since introduction of the Hib vaccine in 2003, with a corresponding increase in non-typeable strains. Non-typeable strains are now the most commonly reported type, with very few reports of types a, b, d, e and f.

Vaccination

Vaccine uptake statistics

Vaccine uptake statistics are published by Public Health Scotland Data and Intelligence.